A fan control unit includes: an internal fan that is provided inside a casing, in which an inverter containing a switching element is disposed, and generates an air current for air-cooling inside the casing; a heat sink which is exposed inside a duct provided on the casing and to which the switching element is attached, the duct being provided with an air-intake port and an air-exhaust port; an air-intake fan disposed at the air-intake port of the duct; an air-exhaust fan disposed at the air-exhaust port of the duct; and a control section performing a control such that the air-exhaust fan is turned on earlier than the air-intake fan and the internal fan as output power increases, and that the internal fan and the air-intake fan are turned off earlier than the air-exhaust fan as output power decreases from a state in which all the fans are kept turned on.