1. An electronic circuit unit comprising:a circuit board having a plate surface;
electronic components mounted on the plate surface of the circuit board; and
an outer case formed on the circuit board by a mold resin, wherein
the circuit board includes a mold exclusion part having a rear surface side covered by the mold resin and a front surface side exposed from the outer case, the front surface side includes a part of the plate surface of the circuit board which is mounted with the electronic components, and a perimeter of the mold exclusion part is covered by the outer case formed by the mold resin, wherein
the outer case is multi-material molded using plural kinds of resin having different fluidities, and wherein
a rear wall of the outer case includes a first portion that covers the rear surface side of the mold exclusion part and a second portion that abuts the first portion, the first portion is made of one of the plural kinds of the resin having a fluidity higher than a fluidity of another one of the plural kinds of the resin constituting the second portion of the outer case,
the mold resin that covers the perimeter of the mold exclusion part is the one of the plural kinds of the resin having the higher fluidity, and
the outer case includes a front portion that covers a portion of the plate surface of the circuit board that is spaced apart from the mold exclusion part, and the front portion is made from the another one of the plural kinds of resin.