In order to improve heat dissipation, the present invention is provided with a plate-like base part 10 having a surface on one side serving as an electronic component contacting surface 11; and a surrounding part 20 which protrudes from peripheral edge sides of the base part 10 while surrounding a space S1 that is on the other side and has the base part 10 as a boundary, wherein the surrounding part 20 has: penetrating long holes 31c; and protruding sections 22 protruding along long edge sections of the long holes 31c from outside the space S1.