The equipment measuring the critical flicker fusion frequency (CFF) is made in order to measure many subjects' CFF at the same time. This equipment is defined the multi-flicker. The equipment measuring CFF, used until now is defined the mono-flicker. It is analysed what factors influence CFF strongly. Then it is made clear that CFF value measured by the multi-f1icker can be used to show the brain weariness as well as that of the mono-flicker, and the vigual angle and the intensity of illumination in the room influence CFF value strongly.