A proximity sensor and proximity sensing method using a change in light quantity of a reflected light are disclosed. The proximity sensor may include a quantity change detection unit which detects a change in a quantity of reflected light which is output light which has been reflected by an object, where an intensity of the output light changes, and a proximity determination unit which determines a proximity of the object to the quantity change detection unit based on a change in the intensity of the output light and the detected change in the quantity of the reflected light.