PURPOSE: To enhance dispersing efficiency by preventing the stagnation of a medium in the treatment tank of a medium dispersing machine.

CONSTITUTION: A rotary cylinder 4 is provided in a treatment tank 1 in a freely rotatable manner so that a narrow treatment space 3 is formed between the wall 2 of the treatment tank and the rotary cylinder and small projections 10... having a parallelogrammic shape are provided to the surface of the rotary cylinder 4. The disc 13 fitted with pins attached to the shaft 11 of the rotary cylinder 4 through a spacer 12 is provided between a treat material supply port 5 of the treatment tank 1 and the rotary cylinder 4 and rotated in close vicinity to the corner part on the supply side 5 of the treatment tank. Therefore, even the medium in the corner part flows positively and is not stagnated within the treatment tank on the supply port side thereof.