A control valve have a main flow passage; a flow passage sectional area adjustment spool; a downstream side branch flow passage; a communicating flow passage; a flow passage opening/closing valve; a flow passage opening/closing spool; and an upstream side branch flow passage. The flow passage opening/closing valve cuts off the downstream side branch flow passage from the communicating flow passage in a low rotation region of an engine. In a medium rotation region, the flow passage opening/closing valve connects the downstream side branch flow passage to the communicating flow passage and the flow passage opening/closing spool allows the communicating flow passage to communicate. In a high rotation region, the flow passage opening/closing spool blocks the communicating flow passage.