To provide a pedestal with a positioning device capable of positioning the position of a material to be mounted with ease and high accuracy.

A pedestal with a positioning device comprises floating support mechanisms 3 having bearing seats 4 provided in the upper surface of a pedestal 2 main body 2 so as to be displaceable in a horizontal plane and supporting the bottom surface of a material to be mounted and energizing means for always applying a return habit to a reference position to the bearing seats 4 and centering mechanisms 5 having centering pins 8 projected or retracted on the upper surface of the pedestal main body 2 and fitted to positioning holes formed on the bottom surface of the material to be mounted which is supported on the pedestal of the floating support mechanisms 3 at the positions where the centering pins 8 protrude. While the material to be mounted is supported on the bearing seats 4 of the floating support mechanisms 3, the centering pins 8 of the centering mechanisms 5 are fitted to the positioning holes formed on the bottom surface of the material to be mounted.