An amplification signal of a difference signal between a sensor signal and an offset signal to be variably set is converted into a digital signal. The sensor signal is in accordance with shake of an imaging device and outputted from a sensor. The first digital signal is obtained while a conversion ratio between the difference signal and the digital signal is set to a first conversion ratio. The second digital signal is obtained while the conversion ratio is set to a second conversion ratio. In relation to a certain difference signal, the value of the second digital signal is smaller than that of the first signal. The offset signal is updated based on the second digital signal. The shake information is generated based on the first digital signal.