An image forming apparatus has at least one replaceable unit replaceably mounted to an image forming apparatus main body. The image forming apparatus outputs a message purporting that a reservation of an operation mode can be received, at the timing that a replacement timing of the replaceable unit which is currently mounted is close in time. If so, prior to the replacement of the replaceable unit which is current mounted, a reservation of an operation mode for a replaceable unit which is to be mounted next time may be received. Further, if the replacement of the replaceable unit is detected, the image forming apparatus starts the control according to the reserved operation mode.