PURPOSE: To detect focus information without decreasing the quantity of light from an imaging optical system by using the light energy from an object in a wavelength region unnecessary for image pickup or the like in detecting the focus information.

CONSTITUTION: A cold filter is used as an optical member 15 for splitting luminous flux so as to split light to the light of the 1st wavelength region necessary for sensitizing a photosensitive member, for example, a photoelectric transducer 4 for television image pickup disposed on the intended focal plane of a photographic lens 2, for example, visible light, and the light of the wavelength region unnecessary for said sensitization, for example, IR light. Since the total quantity of the visible light contributing to the output of the transducer 4 is thus made incident to said transducer 4, the splitting of the luminous flux by the cold filter 14 does not lead to a decrease in the sensitivity of the transducer 4. The focus information is thus detected without decreasing the quantity of light from the imaging optical system.