Provided is a substrate unit including a case accommodating a circuit board; a bus bar electrically connected to the circuit board, and includes an extending portion extending out of the case; and an external thread portion for electrically connecting the extending portion to a connection terminal of a wire harness, the external thread portion including a shaft portion with an external thread, and a head portion that is noncircular, and protrudes at one end portion of the shaft portion in a radial direction of the shaft portion, wherein the case includes a fitting recess to which the head portion is fitted by sliding the external thread portion in a direction intersecting an axial direction of the external thread portion, and that has an abutment surface by which the head portion is stopped, and, at least on the two sides of the abutment surface, relief recesses that define a gap.