A robot hand 23 having a hand body 30 having a reference axis J1 is provided with fixed holding members 40 and 41 and a movable holding member 42. The holding members 40, 41 and 42 are arranged on the hand body at angular intervals about the reference axis J1. Each of the fixed holding members 40 and 41 has a first guide part 50 and a second guide part 51 defining a V-shaped groove. The movable holding member 42 has a first guide part 60 and a second guide part 61 defining a V-shaped groove. Peripheral parts 19 of a wafer 22 are fit in the V-shaped grooves of the holding members 40 to 42 to grip the wafer 22 by the robot hand 23. The first guide parts 50 and 61 are provided at their lower ends with protrusions 55 and 65 protruding toward the reference axis J1, respectively. The protrusions 55 and 65 prevent the wafer 22 from slipping off the holding members 40 to 42.