A head-mounted display device, comprising: a wearable assembly, suitable for wearing to a head of a user; an adjusting module, movably coupled to the wearable assembly, and comprising: a transmission mechanism, movably coupled to the wearable assembly; and a driving element, coupled to the transmission mechanism; and a control module, electrically connected to the driving element, wherein when the control module outputs a control signal to the driving element, the driving element drives the transmission mechanism to actuate, such that the transmission mechanism drives the wearable assembly along with driving of the driving element to change a girth of the wearable assembly to fit heads of different users; and wherein the wearable assembly comprises: a main body, adapted to project a display image to eyes of the user; a headband, connected to the main body, wherein two opposite ends of the headband are overlapped with each other, and the two opposite ends of the headband are adapted to change an overlapping area to change a girth of the headband, so as to fit heads of different users; and a movable casing, movably connected to the headband, wherein the adjusting module is movably coupled to the movable casing and wherein the control module comprises: a micro control unit; a driving circuit unit, electrically connected to the micro control unit and the driving element; and a monitor unit, electrically connected to the micro control unit and between the driving circuit unit and the driving element, and configured to monitor a motor current between the driving circuit unit and the driving element, wherein when the micro control unit determines that the motor current monitored by the monitor unit exceeds a predetermined value, the micro control unit correspondingly stops the driving element through the driving circuit unit. a wearable assembly, suitable for wearing to a head of a user; an adjusting module, movably coupled to the wearable assembly, and comprising: a transmission mechanism, movably coupled to the wearable assembly; and a driving element, coupled to the transmission mechanism; and a transmission mechanism, movably coupled to the wearable assembly; and a driving element, coupled to the transmission mechanism; and a control module, electrically connected to the driving element, wherein when the control module outputs a control signal to the driving element, the driving element drives the transmission mechanism to actuate, such that the transmission mechanism drives the wearable assembly along with driving of the driving element to change a girth of the wearable assembly to fit heads of different users; and wherein the wearable assembly comprises: a main body, adapted to project a display image to eyes of the user; a headband, connected to the main body, wherein two opposite ends of the headband are overlapped with each other, and the two opposite ends of the headband are adapted to change an overlapping area to change a girth of the headband, so as to fit heads of different users; and a movable casing, movably connected to the headband, wherein the adjusting module is movably coupled to the movable casing and wherein the control module comprises: a micro control unit; a driving circuit unit, electrically connected to the micro control unit and the driving element; and a monitor unit, electrically connected to the micro control unit and between the driving circuit unit and the driving element, and configured to monitor a motor current between the driving circuit unit and the driving element, wherein when the micro control unit determines that the motor current monitored by the monitor unit exceeds a predetermined value, the micro control unit correspondingly stops the driving element through the driving circuit unit. a main body, adapted to project a display image to eyes of the user; a headband, connected to the main body, wherein two opposite ends of the headband are overlapped with each other, and the two opposite ends of the headband are adapted to change an overlapping area to change a girth of the headband, so as to fit heads of different users; and a movable casing, movably connected to the headband, wherein the adjusting module is movably coupled to the movable casing and wherein the control module comprises: a micro control unit; a driving circuit unit, electrically connected to the micro control unit and the driving element; and a monitor unit, electrically connected to the micro control unit and between the driving circuit unit and the driving element, and configured to monitor a motor current between the driving circuit unit and the driving element, wherein when the micro control unit determines that the motor current monitored by the monitor unit exceeds a predetermined value, the micro control unit correspondingly stops the driving element through the driving circuit unit. a micro control unit; a driving circuit unit, electrically connected to the micro control unit and the driving element; and a monitor unit, electrically connected to the micro control unit and between the driving circuit unit and the driving element, and configured to monitor a motor current between the driving circuit unit and the driving element, wherein when the micro control unit determines that the motor current monitored by the monitor unit exceeds a predetermined value, the micro control unit correspondingly stops the driving element through the driving circuit unit.