To integrate a double wavelength separation optical system with an infrared detector of each wavelength and to make them mountable on gimbals.

Infrared rays R are received by a main mirror 1a and a submirror 1b and a long wavelength band is reflected like R1 by an infrared filter 1c, while a medium wavelength band R2 is transmitted. The long wavelength band R1 is reflected by a reflector 1d and enters a relay lens 1e, while the medium wavelength band R2 enters a relay lens 1f. The infrared rays are made parallel lights by the relay lenses 1e and 1f respectively and these lights enter the respective vacuum vessels 2a and 3a of infrared detectors 2 and 3 and are led to imaging lenses 2b and 3b, imaged on two-dimensional infrared sensors 2c and 3c and converted into electric signals respectively. Marks 2d and 3d denote coolers. This double wavelength separation optical system and the detectors of the two wavelengths are integrated to be small in size and light in weight and can be mounted on gimbals and, therefore, infrared image homing equipment of an airframe can be realized.