An image forming system includes a main body including a first control part controlling a power mode of the main body and an engine executing image processing, and an operation apparatus receiving an operation for instructing the engine to execute the image processing. The operation apparatus including a second control part controlling a power mode of the operation apparatus. When the operation apparatus receives an instruction to shift the power mode of the main body or the operation apparatus, the first control part determines whether shifting is possible based on a first program executed by the main body and controls a power supply of the main body according to the determination, and the second control part determines whether shifting is possible based on a second program executed by the operation apparatus and controls a power supply of the operation apparatus according to the determination.