The present invention is a part positioning mechanism configured to insert a protruding portion constituting a part of a second sheet metal part into an opening formed in a first sheet metal part. The first contact portion which contacts the first convex portion of the first sheet metal and the second contact portion which contacts the second convex portion of the first sheet metal are disposed to be shifted in an orthogonal direction which intersects orthogonally with the plate thickness direction and an insertion direction for the protruding portion. The edge of the opening of the first sheet metal part has a first edge which is distant from the protruding portion increases from the first convex portion to the second convex portion, and a second edge which is distant from the protruding portion increases from the second convex portion to the first convex portion.