Monitor, display device thereof, monitoring system

A display device for use in a monitor, comprising: a display unit (1) and a support unit (2). The display unit (1) is used for displaying patient-end parameter information. The support unit (2) comprises: an adapter cover (21) and a rotating unit (22) connected onto the adapter cover (21). The display unit (1) is fixedly connected on the rotating unit (22) in a way that allows rotation relative to the rotating unit (22). Also, the monitor, comprising: a master control unit (9) and the display unit (1), where the master control unit (9) is connected to a patient end via at least one cable, and the display unit (1) is detachably connected to the master control unit (9). Also, a monitoring system. With the implementation of the monitor, the display device thereof, and the monitoring system, the display unit (1) rotates and switches while the position of the connecting cable of the master control unit (9) remains unchanged; corresponding marker display areas (3 and 5) and alarm light display areas (4 and 6) are lit up after rotating and switching, thus taking into consideration habits of a user; this is structurally reasonable and facilitates assembly and maintenance.