A wall mounted washing machine and its door opening and closing device and method are provided to increase user convenience in opening and closing a door of the washing machine. The wall mounted washing machine includes a cabinet; a rear panel coupled to the cabinet; a control unit disposed on the front surface of the rear panel with respect to an inner portion of the cabinet; a front panel installed in the tub; a cover installed in the front panel and having a door hinge; a door rotatably coupled to the door hinge and having a door glass; a door opening and closing device adapted for locking or unlocking the door to/from the door; and a control unit disposed on the front surface of the rear panel with respect to an inner portion of the cabinet. The control unit includes a wash controller for controlling washing states; a valve controller for selectively controlling supply of wash water; a door opening and closing controller for controlling the door opening and closing device; and a timer for counting a perio
