Slack is compensated for without causing a wire to slip at a pulley. Provided is a wire driving device (1) including: a pair of wires (17, 18) one ends of which are attached to a movable member (16a) and that antagonistically drive the movable member a pair of pulleys (20, 21) to which the other ends of the individual wires are secured and around which the individual wires are wound a pair of driven gears (22, 23) that are coaxially secured to the individual pulleys a drive gear (24) that is connected to a driving source that generates motive power and a pair of movable gears (25, 26) that are disposed between the drive gear and the individual driven gears and that can transmit the motive power of the driving source to the driven gears from the drive gear, wherein the movable gears are provided in a movable manner so that the movable gears engage with the drive gear and the driven gears when the drive gear is rotated in the direction in which the pulleys take up the wires, and so that the engagements of the movable gears with at least one of the drive gear and the driven gears are released when the drive gear is rotated in the direction in which the pulleys let out the wires.
