An image forming apparatus capable of communicating with the post-processing apparatus. The image forming apparatus includes an execution unit configured to execute a shift processing for shifting the image forming apparatus into a power saving state, a notification unit configured to notify the post-processing apparatus of an instruction to stop supply of power to the post-processing apparatus, and a power control unit configured to control the supply of power to the execution unit. The notification unit is configured, if the supply of power to the notification unit is stopped in a case where the execution unit is executing the shift processing, to control so that power is supplied to the notification unit. The notification unit supplied with power notifies the post-processing apparatus of the instruction.