A hydraulic circuit which, when applied to a turning excavator having hydraulic actuators for the working arms and the turning excavator body supplied with pressure oil from three pumps, can increase the operation speed of the booms and arms without providing a separate hydraulic pump to improve the work efficiency. During the individual driving, the boom cylinder (CY1) is supplied with a pressure oil from the first and third pumps (P1, P3), the arm cylinder (CY2) from the second and third pumps (P2, P3), the bucket cylinder (CY3) from the first pump (P1), and the turning motor (M) from the third pump (P3). During the simultaneous driving of the boom and arm cylinders (CY1, CY2), the arm is supplied with an operation speed increasing pressure oil from the third pump (P3). When the boom cylinder (CY1) and the turning motor (M) are simultaneously operated, a part of the pressure oil to the turning motor (M) from the third pump (P3) is supplied to the boom cylinder (CY2).