A construction machine comprising: a lower track structure; an upper swing structure swingably mounted to the lower track structure; a work device provided on the upper swing structure; a tank reserving a hydraulic operating oil; a single rod-type hydraulic cylinder that drives the work device; a swing hydraulic motor that drives the upper swing structure; an operating device that gives instructions on operations of the work device and the upper swing structure; a first closed circuit pump including a bidirectionally tiltable pump; a second closed circuit pump including a bidirectionally tiltable pump; a cylinder closed circuit that connects the first closed circuit pump to the single rod-type hydraulic cylinder in a state of a closed circuit; a swing closed circuit that connects the second closed circuit pump to the swing hydraulic motor in a state of a closed circuit; a first flushing valve that permits a line on a low pressure side of the cylinder closed circuit to communicate with the tank; a second flushing valve that permits a line on a low pressure side of the swing closed circuit to communicate with the tank; a first selector valve that switches between communication and interruption of communication between the first closed circuit pump and the single rod-type hydraulic cylinder; and a second selector valve that switches between communication and interruption of communication between the second closed circuit pump and the swing hydraulic motor, wherein the construction machine is configured to control openings and closings of the first selector valve and the second selector valve and delivery rates of the first closed circuit pump and the second closed circuit pump according to operation signals inputted from the operating device, and wherein a minimum passage area from the second flushing valve to the tank in a case the second flushing valve is fully open is smaller than a minimum passage area from the first flushing valve to the tank in a case the first flushing valve is fully open, wherein the first flushing valve has a first manifold, a first spool disposed in the first manifold, a first spring (31f1, 31g2) that is disposed in the first manifold and that biases the first spool, and a first shim (31g1, 31g2) disposed between the first spool and the first spring (31f1, 31f2), the second flushing valve has a second manifold, a second spool disposed in the second manifold, a second spring (32f1, 32f2) that is disposed in the second manifold and that biases the second spool, and a second shim (32g1, 32g2) disposed between the second spool and the second spring (32f1, 32f2), and a thickness of the second shim (32g1, 32g2) in a spool axial direction is larger than a thickness of the first shim (31g1, 31g2) in a spool axial direction. a lower track structure; an upper swing structure swingably mounted to the lower track structure; a work device provided on the upper swing structure; a tank reserving a hydraulic operating oil; a single rod-type hydraulic cylinder that drives the work device; a swing hydraulic motor that drives the upper swing structure; an operating device that gives instructions on operations of the work device and the upper swing structure; a first closed circuit pump including a bidirectionally tiltable pump; a second closed circuit pump including a bidirectionally tiltable pump; a cylinder closed circuit that connects the first closed circuit pump to the single rod-type hydraulic cylinder in a state of a closed circuit; a swing closed circuit that connects the second closed circuit pump to the swing hydraulic motor in a state of a closed circuit; a first flushing valve that permits a line on a low pressure side of the cylinder closed circuit to communicate with the tank; a second flushing valve that permits a line on a low pressure side of the swing closed circuit to communicate with the tank; a first selector valve that switches between communication and interruption of communication between the first closed circuit pump and the single rod-type hydraulic cylinder; and a second selector valve that switches between communication and interruption of communication between the second closed circuit pump and the swing hydraulic motor, wherein the construction machine is configured to control openings and closings of the first selector valve and the second selector valve and delivery rates of the first closed circuit pump and the second closed circuit pump according to operation signals inputted from the operating device, and wherein a minimum passage area from the second flushing valve to the tank in a case the second flushing valve is fully open is smaller than a minimum passage area from the first flushing valve to the tank in a case the first flushing valve is fully open, wherein the first flushing valve has a first manifold, a first spool disposed in the first manifold, a first spring (31f1, 31g2) that is disposed in the first manifold and that biases the first spool, and a first shim (31g1, 31g2) disposed between the first spool and the first spring (31f1, 31f2), the second flushing valve has a second manifold, a second spool disposed in the second manifold, a second spring (32f1, 32f2) that is disposed in the second manifold and that biases the second spool, and a second shim (32g1, 32g2) disposed between the second spool and the second spring (32f1, 32f2), and a thickness of the second shim (32g1, 32g2) in a spool axial direction is larger than a thickness of the first shim (31g1, 31g2) in a spool axial direction.