| 摘要 |
A pilot pressure control valve V17 is provided that is switchable between an operation position 56 where pilot pressure is supplied to a first channel switching valve V12 and a non-operation position 57 where pilot pressure is not supplied to the first channel switching valve V12; this pilot pressure control valve V17 is switched to the non-operation position 57 during a state of non-travel and is switched to the operation position 56 with a pilot pressure established in a travel detection circuit 54, and in the operation position 56, supplies a pilot source pressure to the first channel switching valve V12 from a fourth pump P4 on the upstream side of a pressurized oil introduction orifice 53.
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