A projection device and a controlling method of the projection device are provided. The projection device includes a light emitting module, a driver, a light valve, a projection lens and a processor. The light emitting module generates a light beam according to a driving current respectively. The driver generates the driving current and transmit the driving current to the light emitting module according to an operating signal. The light valve receives the light beam to form an image light beam. The projection lens projects the image light beam. The processor provides the operating signal with a default period to the driver and provides an operation of the light valve. According to the operating signal or the operation of the light valve, the driver generates the driving current lower than a default current during a first time interval in the default period.