A humidity controller apparatus includes a refrigerant circuit provided with first and second heat exchangers. The modified USB Series A receptacle connector, according to one embodiment of the invention may include a mechanism such as an additional pin or a mechanical switch to detect the presence of a standard USB Series A plug being inserted into it. The post-injection is immediately interrupted if the quantity of fuel injected reaches the maximum quantity during a stage of returning to idling. In order to increasing data transfer quantity in accordance with a send command issued by a register, a data packet is sent at transfer of an empty packet.