It is designed that an oil pressure signal can be output by operating an
operation lever in a twisting direction; a structure can be made simple
and its assembly and adjustment are easy; an operation force can be
reduced; and a layout is not restricted. It is also designed that when the
operation lever is left free after it is twisted, it returns smoothly to
the original neutral position. When the operation lever is twisted about
the lever axis, the shaft supported by bearings is twisted. The twist of
the shaft is converted into the movement in a direction to move the
pistons by first and second levers, and the pistons are moved. When the
pistons are moved, the oil pressure signal is output from the discharge
ports. A disk plate is separated into a first disk plate to which the root
of the operation lever is attached and a second disk plate which is
tiltably supported by a tilting fulcrum. And, the first disk plate is
independent of the second disk plate and twisted about the lever axis of
the operation lever.