A heat sink-attached power module substrate board comprising a ceramic substrate board; a circuit layer joined on a first surface of the ceramic substrate board; a metal layer joined on a second surface of the ceramic substrate board; and a heat sink joined on the metal layer with heat radiation-side bonding material therebetween, in the heat sink-attached power module substrate board, the circuit layer is a laminated structure having a first layer joined on the first surface of the ceramic substrate board and a second layer joined on a surface of the first layer; the first layer and the metal layer are made of aluminum with purity of not less than 99.99% by mass, the second layer and the heat radiation-side bonding material are made of pure copper or copper alloy, the heat sink is made of aluminum of lower purity than the first layer and the metal layer, where A1 (mm 2 ) is a bonding area of the second layer and the first layer; t1 (mm) is an equivalent board thickness dividing a volume of the second layer by the bonding area A1; σ1 (N/mm 2 ) is an yield strength of the second layer; and α1 (/K) is a linear expansion coefficient of the second layer; where A2 (mm 2 ) is a bonding area of the heat radiation-side bonding material and the metal layer; t2 (mm) is an equivalent board thickness dividing a volume of the heat radiation-side bonding material by the bonding area A2; σ2 (N/mm 2 ) is an yield strength of the heat radiation-side bonding material; and α2 (/K) is a linear expansion coefficient of the heat radiation-side bonding material, and where A3 (mm 2 ) is a bonding area of the heat sink and the heat radiation-side bonding material; t3 (mm) is an equivalent board thickness dividing a volume of the heat sink by the bonding area A3; σ3 (N/mm 2 ) is an yield strength of the heat sink; and α3 (/K) is a linear expansion coefficient of the heat sink, a ratio (A1 × t1 × σ1 × α1)/{(A2 × t2 × σ2 × α2) + (A3 × t3 × σ3 × α3)} at 25°C is not less than 0.70 and not more than 1.30. a ceramic substrate board; a circuit layer joined on a first surface of the ceramic substrate board; a metal layer joined on a second surface of the ceramic substrate board; and a heat sink joined on the metal layer with heat radiation-side bonding material therebetween, in the heat sink-attached power module substrate board, the circuit layer is a laminated structure having a first layer joined on the first surface of the ceramic substrate board and a second layer joined on a surface of the first layer; the first layer and the metal layer are made of aluminum with purity of not less than 99.99% by mass, the second layer and the heat radiation-side bonding material are made of pure copper or copper alloy, the heat sink is made of aluminum of lower purity than the first layer and the metal layer, where A1 (mm 2 ) is a bonding area of the second layer and the first layer; t1 (mm) is an equivalent board thickness dividing a volume of the second layer by the bonding area A1; σ1 (N/mm 2 ) is an yield strength of the second layer; and α1 (/K) is a linear expansion coefficient of the second layer; where A2 (mm 2 ) is a bonding area of the heat radiation-side bonding material and the metal layer; t2 (mm) is an equivalent board thickness dividing a volume of the heat radiation-side bonding material by the bonding area A2; σ2 (N/mm 2 ) is an yield strength of the heat radiation-side bonding material; and α2 (/K) is a linear expansion coefficient of the heat radiation-side bonding material, and where A3 (mm 2 ) is a bonding area of the heat sink and the heat radiation-side bonding material; t3 (mm) is an equivalent board thickness dividing a volume of the heat sink by the bonding area A3; σ3 (N/mm 2 ) is an yield strength of the heat sink; and α3 (/K) is a linear expansion coefficient of the heat sink, a ratio (A1 × t1 × σ1 × α1)/{(A2 × t2 × σ2 × α2) + (A3 × t3 × σ3 × α3)} at 25°C is not less than 0.70 and not more than 1.30. <EOS>