PURPOSE:To enable traveling by means of a manual operation even when an electronic circuit is unable to operate by controlling the output pressure of a solenoid valve which controls the feed of air pressure for an automatic clutch operating actuator, by means of manual operation of an operating knob provided on a driver's seat. CONSTITUTION:Each of the solenoid valves NC1-NC4 and NO1-NO3 of an air control unit EPU is controlled by a CPU, to make air pressure of an air tank AR flow into a pneumatic cylinder CD. As a result, a lever LV1 is operated to control the clutch of a clutch part CL. A manual operating valve is incorporated in an integrated form with the EPU, and is manually controlled by means of an operating knob NB provided on a driver's seat, via a tensile wire TW. Thereby, the output pressure of the solenoid valves is connected to the pneumatic cylinder CD with the knob NB set at the first position I, the connection of the output pressure of the solenoid valves to the pneumatic cylinder is cut off at the second position II and, under this cut-off condition, the input side pressure of the solenoid valves is connected to the pneumatic cylinder at the third position III.
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