1. A surface-coated cutting tool, comprising:a tool body that is made of a tungsten carbide cemented carbide or a titanium carbonitride cermet; and
a hard coating layer that is deposited on a surface of the tool body,
wherein the hard coating layer has a lower layer that is formed on the surface of the tool body and an upper layer that is formed on the lower layer,
(a) the lower layer is made of a Ti compound layer, which has an average total layer thickness of 3 to 20 ?m, and is composed of two or more of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer, the Ti compound layer including at least one TiCN layer,
(b) the upper layer is made of an Al2O3 layer, which has an average layer thickness of 2 to 20 ?m and has an ?-type crystal structure in a chemically deposited state,
(c) regarding Al2O3 crystal grains of the entire upper layer, in a coincidence grain boundary distribution graph showing ratios of coincidence grain boundaries formed of the respective constituent atom-sharing lattice point type, to the whole coincidence grain boundary length in the range of ?3 to ?29, a highest peak is present in ?3 in the range of ?3 to ?29, and a distribution ratio of ?3 in the range of ?3 to ?29 is 70% or more, when electron beams are irradiated to the individual crystal grains in a measurement range of a polished cross-section by using a field-emission-type scanning electron microscope and an electron beam backward scattering diffraction device to measure an orientation of a normal line of each of crystal lattice planes having a corundum hexagonal crystal lattice, a crystal orientation relationship between the adjacent crystal lattices is calculated based on the measurement result, a distribution of lattice points (referred to as constituent atom-sharing lattice points) where each of constituent atoms of a crystal lattice interface shares one constituent atom between the crystal lattices is calculated, and distribution ratios of individuals of ?N+1 are calculated when ?N+1 represents the constituent atom-sharing lattice point type in which there are N lattice points sharing no constituent atoms between the constituent atom-sharing lattice points (here, N is any even number equal to or more than 2 in the corundum hexagonal close-packed crystal structure, but in a case where the upper limit of N is 28 from the viewpoint of distribution frequency, even numbers 4, 8, 14, 24, and 26 do not exist), and
(d) a ratio of a grain boundary having a constituent atom-sharing lattice point type of ?3 continuing from an interface between the lower layer and the upper layer to an outermost surface of the upper layer is 60% or more of a grain boundary having a constituent atom-sharing lattice point type of ?3 distributed in the Al2O3 crystal grains of the entire upper layer, and
wherein an outermost surface layer of the lower layer (a) is made of a TiCN layer having a layer thickness of at least 500 nm or more and contains oxygen only in a depth region with a depth of up to 500 nm from an interface between the TiCN layer and the upper layer, except for oxygen as inevitable impurities, and an average content of the oxygen contained in the depth region is 1 to 3 atom % of a total content of Ti, C, N, and O contained in the depth region.