A cordless blind device for external power drive is provided. The cordless blind device comprises: a winding roll; a screen member wound or unwound on the winding roll; a weight member connected to the lower end of the screen member to apply a torque in the direction in which the screen member is unwound; an elastic member for applying an elastic force to the winding roll to apply a torque in the direction in which the screen member is wound; and a power conversion module formed on at least one of the fixing brackets, and including a first driving shaft connected to the winding roll, a second driving shaft exposed to the outside of the fixing bracket and connected to a driving device connecting hole, and a gear box for transmitting power in both directions between the first driving shaft and the second driving shaft.