PURPOSE: To use both hands for another purpose by attaching a nod switch, which detects the nod angle of a wearer, to a headphone-shaped microphone body.

CONSTITUTION: A light shielding black liquid 44 is sealed in a curved tube 45 while leaving an air bubble 42. A light emitting diode 41 and a photo sensor 43 are provided in one end of the curved tube 45, and light can pass through a transparent window. When the whole of the curved tube 45 is inclined, the air bubble 42 in one end is moved to the other end to intercept the light with the black liquid 44. The photo sensor 43 outputs one pulse when detecting the change from the light detecting state to the light intercepting state. The photo sensor 43 does not output the pulse when detecting the change from the light intercepting state to the light receiving state. Thus, the nod switch counts one nod if the a angle of inclination from the vertical direction to the curve direction exceeds a certain value.