cheek the y direction movement switch 44b is so provided as to contact the part in the vicinity of the operator 39 s left temple the y direction movement switch 44a and the up and down movement switch 42b are mounted on the light shield eye set rings 18a 18b in such a way that the switches 44a 42b pinch the operator 39 s nose the switch 44a is brought into contact with the right side of the nose close to the eyebrow to eyebrow portion and the switch 42b is brought into contact with the left side of the nose close to the eyebrow to eyebrow portion accordingly the vicinity of the eyebrow to eyebrow portion implies the right and left sides of the nose close to the eyebrow to eyebrow portion note that the respective switches 41a 41b 42a 42b 43a 43b 44a 44b involve the use of e g microswitches as push button switches and are constructed to output drive signals during depressions of these switches a strain gauge may be used in place of microswitches given hereinbelow is a detailed explanation of a case where the strain gauge is employed instead of a microswitch the strain gauge exhibits such a nature that an electric resistance varies when a strain is produced when employed as a switch the strain gauge is constructed to detect the variation in the electric resistance and transmit a drive signal to the drive circuit 40 in this case.