An image forming apparatus has an automatic power-off function for automatically shutting off a power source of the image forming apparatus when it is not operated for a predetermined time. A time until the automatic power-off function operates is made different in an ordinary standby mode and an interruption mode. The interruption mode is caused by an abnormality such as no paper. The time period in the interruption mode is made longer than the time period in the standby mode. The time period in the interruption mode is also made variable depending on the type of detected abnormality. The power-off time periods may be extended when an instruction is inputted via an operator. In addition, in an image forming apparatus having an original feeding device, a image forming mode is stored in memory and all the originals which have not been imaged will be ejected before the power is shut off in the interrupt mode.