A shovel, comprising: a lower-part travelling body; a turning mechanism provided on the lower-part travelling body; an upper-part turning body provided on the turning mechanism so as to be turnable relative to the lower-part travelling body; an engine provided in the upper-part turning body; a first hydraulic pump configured to be driven with an output of the engine so as to supply hydraulic oil to a hydraulic actuator of a first system through a first center bypass oil passage; a second hydraulic pump configured to be driven with the output of the engine so as to supply the hydraulic oil to a hydraulic actuator of a second system through a second center bypass oil passage; and a hydraulic circuit configured to selectively supply the hydraulic oil flowing out from at least one of the hydraulic actuator of the first system and the hydraulic actuator of the second system to an intake side or a discharge side of one of the first hydraulic pump and the second hydraulic pump, so that the one of the first hydraulic pump and the second hydraulic pump to whose intake side or discharge side the hydraulic circuit is configured to selectively supply the hydraulic oil flowing out from at least one of the hydraulic actuator of the first system and the hydraulic actuator of the second system operates as a hydraulic motor so as to assist the other of the first hydraulic pump and the second hydraulic pump that operates as a hydraulic pump; wherein a check valve is provided between a tank of the hydraulic oil and the intake side of the one of the first hydraulic pump and the second hydraulic pump to whose intake side or discharge side the hydraulic circuit is configured to selectively supply the hydraulic oil flowing out from at least one of the hydraulic actuator of the first system and the hydraulic actuator of the second system, to prevent the hydraulic oil from flowing to the tank, wherein the hydraulic circuit is configured such that the hydraulic oil selectively supplied to the intake side of the one of the first hydraulic pump and the second hydraulic pump is supplied to a point between the intake side of the one of the first hydraulic pump and the second hydraulic pump and the check valve. a lower-part travelling body; a turning mechanism provided on the lower-part travelling body; an upper-part turning body provided on the turning mechanism so as to be turnable relative to the lower-part travelling body; an engine provided in the upper-part turning body; a first hydraulic pump configured to be driven with an output of the engine so as to supply hydraulic oil to a hydraulic actuator of a first system through a first center bypass oil passage; a second hydraulic pump configured to be driven with the output of the engine so as to supply the hydraulic oil to a hydraulic actuator of a second system through a second center bypass oil passage; and a hydraulic circuit configured to selectively supply the hydraulic oil flowing out from at least one of the hydraulic actuator of the first system and the hydraulic actuator of the second system to an intake side or a discharge side of one of the first hydraulic pump and the second hydraulic pump, so that the one of the first hydraulic pump and the second hydraulic pump to whose intake side or discharge side the hydraulic circuit is configured to selectively supply the hydraulic oil flowing out from at least one of the hydraulic actuator of the first system and the hydraulic actuator of the second system operates as a hydraulic motor so as to assist the other of the first hydraulic pump and the second hydraulic pump that operates as a hydraulic pump;