To provide a technology capable of omitting an actuator by skillfully using capacity of a robot hand.

A moving means 17 with a brake is put in an unrestricted state in a drawing (c). The robot hand 11 is moved to change an interval between first and second gripping parts 13 and 16 to a required interval L1. The brake is applied. At this time, since the second gripping part 16 contacts with a dummy bore 31, the robot hand 11 is moved rightward a little in the drawing (for example, by Δ1) for eliminating this contact. Then, the first and second gripping parts 13 and 16 are moved to a standby position. Thus, since the interval between the first and second gripping parts 13 and 16 is adjusted by a robot, there is no need to arrange the expensive and complicated actuator in a work gripping mechanism so that the work gripping mechanism can be formed as an inexpensive and simple structure.