Dummy holes 36 are made for every one of display dot 5a, 5b and 5c at pixels 5 through interlayer film 33 up to gate electrode and scanning lines 11 before interlayer film 33 on glass substrate 3 is washed. When interlayer film 33 is washed, electric charges stored at semiconductor layer 21 are substantially the same in quantity as those stored at gate electrode and scanning lines 11 through dummy holes 36. Thus, electric potentials at gate electrode and scanning lines 11 are substantially equal in magnitude to those at semiconductor layer 21. This can suppress the occurrence of voltage differences imposed between gate electrode and scanning lines 11 and semiconductor layer 21.