A retractable screen mobile device, comprising: a main unit including a first shell, a first supporting element, and an accommodating space, wherein the first supporting element is disposed on the first shell and has a first supporting surface, and the accommodating space is surrounded and defined by the first shell and the first supporting element; a movable unit slidably disposed on the main unit along a telescopic axis and being capable of converting between a retracted state and an outstretched state with respect to the main unit, wherein the movable unit includes a frame, a pivot shaft, at least one hook, a second supporting element, a steering shaft, and a moving plate, and wherein the pivot shaft is disposed on one side of the frame away from the first shell, the at least one hook is pivotally hung on the pivot shaft, the second supporting element is pivotally connected to the at least one hook and has a second supporting surface, the second supporting element is able to switch between a lower position and an aligned position with respect to the pivot shaft, the steering shaft is connected to the frame and accommodated in the accommodating space, and the moving plate partially covers the first shell; at least one elastic member with two ends respectively disposed on the first shell and the moving plate, and tends to keep the movable unit in either the retracted state or the outstretched state; a flexible display screen including a first end and a second end, wherein the first end is disposed on the first supporting element and the second end is fixed to the first shell, and wherein the flexible display screen covers the first supporting surface, winds around the pivot shaft to change direction, and winds around the steering shaft to change direction again; and at least one constant force spring including a winding part and a telescopic part, wherein the winding part is disposed on the first shell, and the telescopic part is disposed on the frame for constantly providing a pulling force on the frame, so that the steering shaft disposed on the frame constantly tightens the flexible display screen; wherein the pivot shaft and the first shell are closest to each other when the movable unit is in the retracted state, and the pivot shaft and the first shell are farthest away from each other when the movable unit is in the outstretched state. a main unit including a first shell, a first supporting element, and an accommodating space, wherein the first supporting element is disposed on the first shell and has a first supporting surface, and the accommodating space is surrounded and defined by the first shell and the first supporting element; a movable unit slidably disposed on the main unit along a telescopic axis and being capable of converting between a retracted state and an outstretched state with respect to the main unit, wherein the movable unit includes a frame, a pivot shaft, at least one hook, a second supporting element, a steering shaft, and a moving plate, and wherein the pivot shaft is disposed on one side of the frame away from the first shell, the at least one hook is pivotally hung on the pivot shaft, the second supporting element is pivotally connected to the at least one hook and has a second supporting surface, the second supporting element is able to switch between a lower position and an aligned position with respect to the pivot shaft, the steering shaft is connected to the frame and accommodated in the accommodating space, and the moving plate partially covers the first shell; at least one elastic member with two ends respectively disposed on the first shell and the moving plate, and tends to keep the movable unit in either the retracted state or the outstretched state; a flexible display screen including a first end and a second end, wherein the first end is disposed on the first supporting element and the second end is fixed to the first shell, and wherein the flexible display screen covers the first supporting surface, winds around the pivot shaft to change direction, and winds around the steering shaft to change direction again; and at least one constant force spring including a winding part and a telescopic part, wherein the winding part is disposed on the first shell, and the telescopic part is disposed on the frame for constantly providing a pulling force on the frame, so that the steering shaft disposed on the frame constantly tightens the flexible display screen; wherein the pivot shaft and the first shell are closest to each other when the movable unit is in the retracted state, and the pivot shaft and the first shell are farthest away from each other when the movable unit is in the outstretched state.