The thin film transistor includes: a gate electrode formed on a surface of a substrate; a polysilicon layer formed on an upper side of the gate electrode; an amorphous silicon layer formed on the polysilicon layer so as to cover the same; an n+ silicon layer formed on an upper side of the amorphous silicon layer; and a source electrode and a drain electrode which are formed on the n+ silicon layer, wherein, in a projected state in which the polysilicon layer, the source electrode and the drain electrode are projected onto the surface of the substrate, a part of the polysilicon layer and a part of each of the source electrode and the drain electrode are adapted so as to be overlapped with each other, and in the projected state, a minimum dimension, in a width direction orthogonal to a length direction between the source electrode and the drain electrode, of the polysilicon layer located between the source electrode and the drain electrode is smaller than dimensions in the width direction of the source electrode and the drain electrode.