PURPOSE:To perform transmission of light in an easy and efficient manner in a unit which performs the light transmission between a photo signal generating means and a photo signal processing means which are disposed on the upper and the lower side of a steering wheel by providing a light guide passage at a part of said wheel where a light transmission path is cut off. CONSTITUTION:A pad 2 is disposed at the upper and middle site of the upper part of a steering wheel 1 and a light transmission and receival processing part 3 is disposed at the lower site thereof which is on the side of a car body. A photo switch device 4 which is a photo signal generating means and a light guide passage 5 which transmits light thereto are included in said pad 2. On the other hand, a luminescent element 7 and a light receiving element 8 are included in the processing part 3 and face to light guide passages 9 and 10 which opposed to the light-in end 5a and a light-out end 5b of the light guide passage 5, respectively. Light guide passage 11 are formed in the wheel 1 at the positions where a spoke 1c thereof meets the lights paths. The spoke 1c may therefore be prevented from cutting off the light paths and the desired purpose be attained.