According to the present invention, in the case where the amount of ink remaining in an ink tank is detected using light from a light emitting unit, whether or not the amount of remaining ink is smaller than a predetermined value can be accurately determined with a decrease in the life of the light emitting unit suppressed. Thus, the present invention determines a difference between output signals each output by the light receiving unit according to a corresponding one of at least two of a plurality of levels of light emissions from the light emitting unit. Based on the difference, whether or not the amount of remaining ink is smaller than the predetermined value is determined.