3 constituting a lens system protrudes from a rectangular main body portion 2 brackets 4 extend from the main body portion 2 and an attachment hole 4 a is provided in each bracket 4 at a distal end thereof the left and right infrared cameras 1 l 1 r are transversely symmetrical with each other with respect to directions in which the brackets extend as shown in fig5 a backside of the infrared camera 1 l is confronted with the back plate 33 of the sensor bracket 31 l and is then fixed thereto via one reference support member 35 and two adjustable support members 36 37 the reference support member 35 is something like a rectangular prism with a predetermined longitudinal length a bolt hole 35 a penetrates longitudinally through the rectangular prism and an engagement pin 35 b protrudes upwardly along a backside of the reference support member 35 further an engagement pawl is formed on an upper end of the engagement pin 35 b the adjustable support members 36 37 respectively include attachment tab portions 36 a 37 a provided on left and right hand sides of rectangular prism cases of the adjustable support members 36 37 in such a manner as to protrude therefrom and threaded rods 36 b 37 b protrude from front sides of the respective rectangular prism cases while adjustment pins 36 c 37 c protrude upwardly from upper sides of the respective cases incorporated in.