Insulating circuit board and insulating circuit board provided with cooling sink section

An insulating circuit board is provided with an insulating board, a circuit board bonded to a first plane of the insulating board, and a metal plate bonded to a second plane of the insulating board. The circuit board is formed of an Al alloy having a purity of 99.98% or pure Al, and the metal plate is formed of an Al alloy having a purity of 98.00% but not more than 99.90%. A thickness (a) of the circuit board is, for instance, 0.2mm or more but not more than 0.8mm, and a thickness (b) of the metal plate is, for instance, 0.6mm or more but not more than 1.5mm, and an inequality of a/b=1 is satisfied. An insulating circuit board provided with a cooling sink section has the insulating circuit board, and a cooling sink section bonded to the metal plate through a second solder layer. The second solder layer is formed of a solder having Sn as a main ingredient, with a Young's modulus of, for instance, 35GPa or more, a 0.2% proof strength of, for instance, 30MPa or more, and a tensile strength of, for instance, 40MPa or more. The cooling sink section is formed of, for instance, pure Al or an Al alloy.