1. A synapse element comprising a transistor set made of a first MIS (metal insulator semiconductor) transistor having a first gate electrode and a second MIS transistor having a second gate electrode, the second MIS transistor connecting in series with the first MIS transistor, in which an effective &bgr;-value of the transistor set is adjusted by voltage of a first input signal provided to the first gate electrode, and the transistor set is switched according to a second input signal provided to the second gate electrode.