In an image forming apparatus, a first detection part and a second detection part, each for detecting a position of a displacement member that changes its position according to a remaining amount of liquid in a sub-tank, are provided to a carriage carrying the sub-tank and a recording head, and a body of the image forming apparatus, respectively. A first position is a position of the displacement member detected by the first detection part such that the remaining amount of liquid in the sub-tank is smaller than that at a second position detected by the second detection part. The liquid is supplied to the sub-tank of a differential supply amount, corresponding to a displacement amount of the displacement member between a position detected by the first detection part and a position detected by the second detection part, after the first detection part detects the displacement member.