An apparatus for supplying a constant amount of abrasive which can supply even dry ice particles, ice particles, or the like as abrasive in a constant amount is provided. In order to take out abrasive contained in measuring holes 21 of a rotating disc 20, an abrasive mixing section 40 for blowing a compressed gas into each of the measuring holes 21 has a cylinder 41′ which opens toward one surface of the rotating disc at the position where the measuring holes are formed. A piston 43′ is inserted into the cylinder. A fluid channel 45 opens toward the cylinder 41′ through the intermediary of the rotating disc 20 and whose opening rim 45a is in sliding contact with another surface of the rotating disc 20. One of the cylinder 41′ and the fluid channel 45 communicates with a compressed-gas supply source through the intermediary of a compressed-gas introduction path 52. The other one of the cylinder 41′ and the fluid channel 45 communicates with the abrasive transport path 51. The piston 43′ has a through-hole 43a passing therethrough in such a manner as to coincide with the position where the measuring holes are formed.