An operation panel 30 is provided with a plurality of operation buttons 36.
A string-like resistor body 41 is held in a resistor holding plate 31. The
resistor body 41 has a tube-like elastic outer resistor member 42, an
inner resistor member 43 loosely arranged within the outer resistor member
and insulating spacers 44 arranged between the inner resistor member and
the outer resistor member at predetermined intervals in the longitudinal
direction of the inner resistor member so that the inner periphery of the
outer resistor member 42 and outer periphery of the inner resistor member
43 are constantly separated from each other. A control unit 53 is provided
to produce an operation signal.
