A heat sink-attached power module substrate board has 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, where A1 (mm2) is a bonding area of a second layer and a first layer composing a circuit layer; t1 (mm) is an equivalent board thickness, σ1 (N/mm2) is yield strength, and α1 (/K) is a linear expansion coefficient, all of the second layer, where A2 (mm2) is a bonding area of the heat radiation-side bonding material and the metal layer; t2 (mm) is equivalent board thickness, σ2 (N/mm2) is yield strength, and α2 (/K) is a linear expansion coefficient, all of the heat radiation-side bonding material, and where A3 (mm2) is a bonding area of the heat sink and the heat radiation-side bonding material; t3 (mm) is equivalent board thickness, σ3 (N/mm2) is yield strength, and α3 (/K) is a linear expansion coefficient, all of the heat sink.