A straight traveling hydraulic circuit is disclosed, which, in the case of performing a combined operation in which working and traveling devices are simultaneously driven, can prevent a declination of equipment due to an overload of the working devices. The straight traveling hydraulic circuit includes first and second variable hydraulic pumps, a left traveling motor and a first working device connected to the first hydraulic pump, switching valves installed in a flow path of the first hydraulic pump, a right traveling motor and a second working device connected to the second hydraulic pump, switching valves installed in a flow path of the second hydraulic pump, a straight traveling valve installed in the flow path of the second hydraulic pump, and a control valve installed in a branch flow path branched from the flow path of the second hydraulic pump. The straight traveling valve is shifted to supply the hydraulic fluid from the first hydraulic pump to the left and right traveling motors and to supply the hydraulic fluid from the second hydraulic pump to the first and second working devices. The control valve connects inlet and outlet parts of the straight traveling valve, and is shifted, when the combined operation is performed, to intercept a supply of the hydraulic fluid from the second hydraulic pump to the traveling motor.