An exemplary manipulator of a robot includes a fastening seat defining two guiding grooves, a driving mechanism disposed on the fastening seat, two transmitting plates respectively received in the two guiding grooves and cooperating with the driving mechanism, and two detecting bars each fixedly connecting with a corresponding transmitting plate. A detecting pin is fixed on each of the detecting bars. Under a driving action of the driving mechanism on the transmitting plates, the transmitting plates are activated to slide in the guiding grooves to cause the detecting bars to move close to or apart from each other, whereby a distance between the two detecting pins is automatically regulated.