To operate an operating cord of a window blind without directly pulling the operating cord.

This operating device of a window blind includes a pulley 26 wrapped around with the suspended portion of the looped operating cord 16 suspended from a head box 10 for lifting or opening and closing a slat 14, a motor 30 capable of rotatingly driving the pulley 26, an operation switch 32 capable of switching the motor 30 between the electrified state and the non-electrified state, and an operation case 28 for supporting the pulley 26 and the motor 30 in such a manner that the pulley and the motor can be relatively moved in the vertical direction. When the operation case 28 is pushed downward, the operation switch 32 is switched to electrify the motor 30 by the relative movement of the operation case 28 and the pulley 26 and the motor 30, the pulley 26 is rotated, and the operation cord 16 is electrically operated.