According to the present invention, even in the case of addition of a transformer for using an engine system with an AC power supply different from the expected voltage of an electrical device, there is substantially no change in the thermal balance in a package due to the presence or absence of the transformer. In the present invention, an engine 2 and an electrical device for driving the engine system are housed in a package 1. In order for a transformer 20 whose primary side is an AC power supply and whose secondary side is the expected voltage of the electrical device for driving the engine system to be housed in the package, an intake port, an exhaust port, and a ventilation fan for cooling the transformer are provided in a ventilation path that is independent from other devices.