An image forming system includes: an image former that forms an image; a stacker that stacks a recording medium on which an image has been formed by the image former and which has been discharged from the image former; a lifter that raises or lowers the stacker between a stacking position where the recording medium is stacked and a lower position located below the stacking position; a recording medium detector that detects the recording medium stacked on the stacker; and a hardware processor that controls driving of the lifter so as to lower the stacker from the stacking position to the lower position when it is determined that the recording medium is on the stacker on the basis of a detection result of the recording medium detector within start-up time from a time when power is switched on to a time of shifting to an image formable state.