A recording-medium-residual-quantity detecting device includes a first rotation-quantity detecting unit that detects a rotation quantity of a roll in which a recording medium is wound. A second rotation-quantity detecting unit detects a rotation quantity of a transportation roller that transports the recording medium by rotating in contact with the recording medium that is unwound from the roll. A controlling unit has a winding control mode in which driving units of the device are controlled so that rotational powers to wind the recording medium into the roll without slack between the roll and the transportation roller are applied to the roll and the transportation roller. The residual quantity of the recording medium is calculated on the basis of a rotation quantity θr of the roll and a rotation quantity θs of the transportation roller that are respectively detected by the rotation-quantity detecting units when the winding control mode is executed.