An insulated circuit board which is obtained by bonding a circuit layer onto one side of a ceramic substrate, and bonding a metal layer made of copper or copper alloy onto the other side of the ceramic substrate; and a heat sink which is bonded to the metal layer are included; the heat sink has a first metal layer made of aluminum or aluminum alloy joined to the metal layer, a ceramic board material joined to the first metal layer at an opposite side to the metal layer, and a second metal layer made of aluminum or aluminum alloy joined to the ceramic board material at an opposite side to the first metal layer; a thickness T1 of the first metal layer and a thickness T2 of the second metal layer are 0.8 mm to 3.0 mm inclusive; and a thickness ratio T1/T2 is 1.0 or more.