1. A board unit comprising:a circuit board;
a case having a peripheral wall for accommodating the circuit board, the peripheral wall including a pair of side walls, a front wall and a back wall;
a bus bar electrically connected to the circuit board and having a lead-out part which extends out of the case;
a power terminal connecting the lead-out part of the bus bar with a connection terminal of an electric wire; and
a cover assembled to the case from above so as to cover the power terminal and having a lateral wall, which overlaps a corresponding lateral surface of one of the pair of side walls and on an outer side thereof,
wherein one of the pair of side walls and the lateral wall of the cover is provided with an engagement protrusion protruding outwardly with respect to the cover, and the other of the one of the pair of side walls of the case and the lateral wall of the cover is provided with an engagement recess to be engaged with the engagement protrusion,
wherein the lateral wall of the cover is provided with a latch piece at a position that is axially offset from the engagement protrusion or the engagement recess in a longitudinal direction defining a longitudinal length of the lateral wall, and the one of the pair of side walls of the case is provided with a latch portion to be latched with the latch piece, the engagement protrusion and the latch portion being coplanar with each other on the lateral wall, and
wherein latching between the latch piece and the latch portion restricts displacement of the lateral wall of the cover with respect to the case.