[Objective] To provide a wafer carrier measuring jig which can measure a slot height of a wafer carrier placed on a load port and which can determine whether or not an arbitrary slot is horizontal, a collision preventing jig, and a collision preventing method using the collision preventing jig.[Means for Solution] A wafer carrier measuring jig includes a base member 21 having a carrier placement section 210 where three kinematic pins 211 are disposed in correspondence with three V-shaped grooves provided on the bottom surface of a wafer carrier 10 having a pair of slot sections 12 where wafers 11 are accommodated; a measuring means 22 fixedly provided on the base member 21 and having sensors 250 for measuring height from a predetermined reference value, slot pitch, and slot horizontality with respect to at least some slots in the two slot sections 12; and a write means provided in the carrier placement section 210 of the base member 21 and adapted to write information from the measuring means 22 to an ID information storage means provided in the wafer carrier 10.