A phase change memory (PCM) in which the phase change storage element is crystallized by a gradually increasing/decreasing operating current. The PCM comprises a switching circuit, the phase change storage element, a bit select switch, a pulse generating module, and a counting module. The switching circuit comprises a plurality of switches, selectively providing branch paths to an output terminal of a current source. The bit select switch controls the conduction between the phase change storage element and the output terminal of the current source. The pulse generating module outputs a pulse signal oscillating between high and low voltage levels. When enabled, the counting module counts the oscillations of the pulse signal, and outputs the count result by a set of digital data. The set of digital data are coupled to the switching circuit to control the switches therein.