The purpose of the present invention is to obtain improved heat dissipation performance using a shape that enables space to be saved. The present invention comprises a plate-shaped base part 10 in which the surface on one side is an electronic component contact surface 11, and a surrounding part 20 that projects from the peripheral edge side of the base part 10 so as surround an internal space S2 on the other side across the base part 10. The surrounding part 20 is provided with ventilation holes 21a by which the internal space S2 communicates with an exterior space S1 beside the surrounding part 20. Projecting pieces 22 projecting toward the internal space S2 side are provided to the inner edges of the ventilation holes 21a.