According to embodiments, there is provided an electronic component unit, including: a circuit board including: a heat generating element that generates a heat; and a bonding metal foil layer formed on a face thereof; a heat transfer board including: a board body having a thermal conductivity higher than that of the circuit board; an insulative layer formed on a first face of the board body; and a heat transfer metal foil layer formed to cover the insulative layer; and a heat sink, wherein the circuit board is assembled with the heat sink via the heat transfer board such that (1) the heat transfer metal foil layer is soldered to the bonding metal foil layer and (2) the second face of the board body is superimposed on the heat sink.