A tower crane includes a tower on which a rotating portion is pivotally mounted and configurable between a service configuration in which the rotating portion can be rotatably driven by a motorized orientation system, and an out of service configuration in which the rotating portion is rotatably released to be able to be oriented in the direction of the wind. A control/command unit activates a monitoring mode in the out of service configuration to detect, depending on variations in the angle of orientation or the angular speed of the rotating portion, if the rotating portion is in one of the following movement states: an autorotation state corresponding to a rotary movement of the rotating portion in a given direction over at least one complete turn; or an oscillation state corresponding to a back and forth movement of the rotating portion about the orientation axis.