A chain saw as a power tool includes a combustion engine and an electric motor. The chain saw has a driving shaft which drives a saw chain, a battery pack which provides electric current to the electric motor, and a controller which is connected to the battery pack. In the chain saw, both the combustion engine and the electric motor drive the driving shaft so that the driving shaft drives the saw chain. Further, the controller controls a driving of the electric motor based on a remaining capacity of the battery pack.