An image sensing apparatus comprises: a pixel unit; a generator that generates and outputs a plurality of reference signals having different slopes from each other that increase in proportion to elapsation of time; a selector that selects one of the plurality of reference signals; and an analog-to-digital converter that converts an analog signal outputted from the pixel unit of an image sensor to a digital signal using the reference signal selected by the selector, wherein the generator generates the plurality of reference signals in parallel, and in a case where an analog signal of a reset level is outputted from the pixel unit, the selector changes the reference signal selected from the plurality of reference signals each time the selected reference signal exceeds the analog signal.