A power module apparatus (10) comprises: a power module (100A) comprising a package (110) configured to seal a perimeter of a semiconductor device, and a heat radiator (42) bonded to one surface of the package; a cooling device (30) comprising a coolant passage (33) through which coolant water flows, in which the heat radiator is attached to an opening (35) provided on a way of the coolant passage, wherein the heat radiator (42) of the power module (100A) is attached to the opening (35) of the cooling device (30) so that a height (ha) and a height (hb) are substantially identical to each other. The power module in which the heat radiator is attached to the opening formed at the upper surface portion of the cooling device can also be efficiently cooled, and thereby it becomes possible to reduce degradation due to overheating.