To provide a hydraulic circuit which can easily change a hydraulic pressure source of a service port between a uniflow type and a confluence type and can prevent engine load from being increased when a direction control valve is at a neutral position.

The hydraulic circuit includes first, second and third pumps 14, 15, 16 each for delivering hydraulic oil, and the three-position six-port direction control valve 23 for manipulating an attachment which is incorporated in a hydraulic fluid feed system of the second pump 15. Both secondary ports except for a pressure fluid passing port of the direction control valve 23 are connected to the service port 22. The hydraulic circuit is provided with a flow switching valve 30 which can be alternatively set at a confluence position for communicating with the most downstream portion of a hydraulic fluid feed system of the third pump 16 to both primary ports except for a tank port of the direction control valve 23 and including a pressure fluid inflow port or at a uniflow position for communicating the most downstream portion of the hydraulic fluid feed system of the third pump to a hydraulic fluid tank 31.