A cable system A includes a cable 3 for connecting a base device 1 and a travelling body 2, a reel device 10 mounted on the travelling body 2, a motor controller 40 for controlling a motor 15 of the reel device 10, and a rotary encoder 16 (rotation sensor) for detecting rotation of a reel 12. The motor controller 40 basically makes the motor 15 free, when the reel 12 is rotating in an unreeling direction, and basically applies a rotational torque in a reeling direction to the reel 12, when the reel 12 is rotating in the reeling direction. Furthermore, even if the reel 12 is rotating in the unreeling direction, if an unreeling speed of the cable 3 exceeds a travelling speed of the travelling body 2, the rotational torque in the reeling direction is applied to the reel 12. Slackening of the cable 3 is thereby prevented.