A manufacturing method of a group III-V compound semiconductor device, the method includes: a first process in which a group V material gas and an impurity material gas are supplied to a reacting furnace which is set at a first temperature of a range from 400° C. to 500° C. and a first pressure of a range from 100 hPa to 700 hPa, and impurities are doped in an undoped group III-V compound semiconductor layer, and a second process in which the supply of the impurity material gas is stopped, a temperature of the reacting furnace is raised to a second temperature which is higher than the first temperature, a pressure of the reacting furnace is set lower than a pressure of the first pressure, a supply of an etching gas is initiated and the supply of the group V material gas is continued.