A part positioning mechanism comprising a first and a second sheet metal part, the part positioning mechanism being configured to position a first sheet meta part and a second sheet metal part by inserting a protruding portion constituted by a part of the second sheet metal part into an opening formed in the first sheet metal part, wherein in a state of the protruding portion being inserted into the opening and being positioned, the first sheet metal part has a first convex portion (1b, 1c) and a second convex portion (1e, 1f), which protrude from an edge of the opening and position the protruding portion by sandwiching the protruding portion in a plate thickness direction, which is a direction of the plate thickness of the second sheet metal part, the protruding portion has a first contact portion which contacts the first convex portion (1b, 1c), and a second contact portion which contacts the second convex portion (1e, 1f) on the opposite side to the side of the first contact portion, the first contact portion and the second contact portion are disposed with a gap in an orthogonal direction which intersects orthogonally with the plate thickness direction and an insertion direction in which the protruding portion is inserted into the opening, and the edge of the opening has a first edge which is an edge of the opening on the side facing the first contact portion, and of which distance from the protruding portion increases in the orthogonal direction from the first convex portion (1b, 1c) to the second convex portion (1e, 1f), and a second edge which is an edge of the opening on the side facing the second contact portion, and of which distance from the protruding portion increases in the orthogonal direction from the second convex portion (1e, 1f) to the first convex portion (1b, 1c). wherein in a state of the protruding portion being inserted into the opening and being positioned, the first sheet metal part has a first convex portion (1b, 1c) and a second convex portion (1e, 1f), which protrude from an edge of the opening and position the protruding portion by sandwiching the protruding portion in a plate thickness direction, which is a direction of the plate thickness of the second sheet metal part, the protruding portion has a first contact portion which contacts the first convex portion (1b, 1c), and a second contact portion which contacts the second convex portion (1e, 1f) on the opposite side to the side of the first contact portion, the first contact portion and the second contact portion are disposed with a gap in an orthogonal direction which intersects orthogonally with the plate thickness direction and an insertion direction in which the protruding portion is inserted into the opening, and the edge of the opening has a first edge which is an edge of the opening on the side facing the first contact portion, and of which distance from the protruding portion increases in the orthogonal direction from the first convex portion (1b, 1c) to the second convex portion (1e, 1f), and a second edge which is an edge of the opening on the side facing the second contact portion, and of which distance from the protruding portion increases in the orthogonal direction from the second convex portion (1e, 1f) to the first convex portion (1b, 1c).