A crane, comprising: a hydraulic circuit including a hydraulic pump , a hydraulic motor , and a control valve having a neutral free position (N), the hydraulic pump and the hydraulic motor being connected through the control valve ; an upperstructure driven to swing by the hydraulic motor; a swing control device controlling the control valve for swing operation of the upperstructure ; a swing brake device installed between the hydraulic motor and the control valve and having a brake control valve (4a, 4b; 304) that limits a flow of oil on a return side of the hydraulic motor to at least an open and a closed flow, whereas for any flow other than an open flow, the swing brake device limiting oil on the return side of the hydraulic motor to generate a hydraulic braking force; a first backpressure detector detecting a motor backpressure between the brake control valve and one of ports of the hydraulic motor as a first motor backpressure; a second backpressure detector detecting a motor backpressure between the brake control valve and the other port of the hydraulic motor as a second motor backpressure; and characterized by a notification device ; a control device having an external-force direction estimation unit that estimates a swing direction of the upperstructure under an external force acting on the upperstructure on the basis of the first motor backpressure and the second motor backpressure during an operating state of the swing brake device , and a notification control unit that causes the notification device to provide notification of the estimated swing direction of the upperstructure . a hydraulic circuit including a hydraulic pump , a hydraulic motor , and a control valve having a neutral free position (N), the hydraulic pump and the hydraulic motor being connected through the control valve ; an upperstructure driven to swing by the hydraulic motor; a swing control device controlling the control valve for swing operation of the upperstructure ; a swing brake device installed between the hydraulic motor and the control valve and having a brake control valve (4a, 4b; 304) that limits a flow of oil on a return side of the hydraulic motor to at least an open and a closed flow, whereas for any flow other than an open flow, the swing brake device limiting oil on the return side of the hydraulic motor to generate a hydraulic braking force; a first backpressure detector detecting a motor backpressure between the brake control valve and one of ports of the hydraulic motor as a first motor backpressure; a second backpressure detector detecting a motor backpressure between the brake control valve and the other port of the hydraulic motor as a second motor backpressure; and a notification device ; a control device having an external-force direction estimation unit that estimates a swing direction of the upperstructure under an external force acting on the upperstructure on the basis of the first motor backpressure and the second motor backpressure during an operating state of the swing brake device , and a notification control unit that causes the notification device to provide notification of the estimated swing direction of the upperstructure . <EOS>