A thin film transistor includes a one conductive type semiconductor layer (11); a source region (12) and a drain region (13) which are separately provided in the semiconductor layer; and a gate electrode (14) provided above or below the semiconductor layer with an insulating film interposed therebetween, wherein the width (Ws) of the junction face between the source region and the channel (16) which is provided between the source region and drain region, is different from the width (Wd) of the junction face between the above channel region and the drain region.