To read out a flicker value directly by detecting brightness on the surface of an object, i.e., a liquid crystal panel, normalizing an obtained brightness signal and generating a flicker value from the AC component thereof.

A photosensor 10 located in proximity to an object, i.e., the screen of a liquid crystal panel 1, detects light from the screen face to produce a brightness signal which is then amplified through an amplifier 21. At that moment of time, the brightness signal has a DC component and an AC component wherein the DC component is the panel face brightness component and the AC component is the flicker component. The amplified brightness signal is normalized through an AGC circuit 22 with respect to a reference value through automatic gain control. AC component in the normalized brightness signal is then separated by an AC component separation circuit 23 and detected by a detection circuit 24. A DC voltage representative of the peak-to-peak value of the AC component is thereby generated and used by an indicator 30 for indicating a flicker value. According to the arrangement, the flicker value can be read out directly.