To provide a field effect transistor (FET) improved in functionality, and a logical circuit using the transistor.

The FET 100 includes a channel region 16 changeable in polarity, and a ferroelectric region 26 provided near the channel region 16 and changing the polarity of the channel region 16 based on the own polarization state. The FET 100 further includes a first control means 24 controlling the carrier density of the channel region 16, and a second control means 12 changing the polarization state of the ferroelectric region 26. The polarization state of the ferroelectric region 26 is changed by a control signal Vc applied to the first control means 24, and as a result, the polarity of the channel region 16 can be changed. The polarity of the FET 100 can thereby be optionally changed, and the once changed polarity of the FET 100 can be maintained even after power-off.