A power module, comprising: a sealed body including a semiconductor device, a first lead frame (315, 316) coupled to one of front and back electrode surfaces of the semiconductor device with a metal joining material between them, a second lead frame (318, 319) coupled to the other one of front and back electrode surfaces of the semiconductor device with the metal joining material between them, and a sealing material with which the semiconductor device, first lead frame (315, 316), and second lead frame (318, 319) are sealed; and further comprising a module housing that accommodates the sealed body and has a housing base with an opening formed therein and a cover shaped to close the opening; a first insulating heat sink disposed between the sealed body and an internal wall of the housing base; and a second insulating heat sink disposed between the sealed body and cover, wherein the first lead frame (315, 316) is bared out of the sealing material, and the bared surface of the first lead frame (315, 316) is in contact with the first insulating heat sink; the second lead frame (318, 319) is bared out of the sealing material, and the bared surface of the second lead frame (318, 319) is in contact with the second insulating heat sink; the module housing has a cover receiving part formed on the perimeter of the opening; the cover has a part thereof, which is opposed to the second insulating heat sink, formed as a projection that juts out toward the sealed body side, and the cover is fixed to the cover receiving part; at least one of the first insulating heat sink and second insulating: heat sink is formed so that the thickness thereof varies depending on a predetermined or stronger pressing force, and at least one of the first insulating heat sink and second insulating heat sink is pressed against the sealed body with the thickness thereof varied with the pressing force from the projection of the cover. a sealed body including a semiconductor device, a first lead frame (315, 316) coupled to one of front and back electrode surfaces of the semiconductor device with a metal joining material between them, a second lead frame (318, 319) coupled to the other one of front and back electrode surfaces of the semiconductor device with the metal joining material between them, and a sealing material with which the semiconductor device, first lead frame (315, 316), and second lead frame (318, 319) are sealed; and further comprising a module housing that accommodates the sealed body and has a housing base with an opening formed therein and a cover shaped to close the opening; a first insulating heat sink disposed between the sealed body and an internal wall of the housing base; and a second insulating heat sink disposed between the sealed body and cover, wherein the first lead frame (315, 316) is bared out of the sealing material, and the bared surface of the first lead frame (315, 316) is in contact with the first insulating heat sink; the second lead frame (318, 319) is bared out of the sealing material, and the bared surface of the second lead frame (318, 319) is in contact with the second insulating heat sink; the module housing has a cover receiving part formed on the perimeter of the opening; the cover has a part thereof, which is opposed to the second insulating heat sink, formed as a projection that juts out toward the sealed body side, and the cover is fixed to the cover receiving part; at least one of the first insulating heat sink and second insulating: heat sink is formed so that the thickness thereof varies depending on a predetermined or stronger pressing force, and at least one of the first insulating heat sink and second insulating heat sink is pressed against the sealed body with the thickness thereof varied with the pressing force from the projection of the cover.