To provide a horizontal wet type medium agitating dispersion grinder capable of quickening a grinding speed of material to be ground, reducing a power consumption and dissolving the deviation of a medium for grinding in a grinding room.

The horizontal wet type medium agitating dispersion grinder 20 is provided with the grinding room 21 of the length L and diameter D having a relation L/D≤1.25 inside a horizontal flow pipe. The grinding room 21 is provided with supply ports 22 of treated slurry disposed on left and right thereof, discharge ports 23 (23a, 23b) of discharging the treated slurry after treatment on a central circumferential part, an agitation shaft 24 inside the grinding room, an impeller 26 fixed and arranged on the center of the agitation shaft 24 and two sheets of perforated agitation disks 25 with pin respectively fixed and arranged on the left and right. In the grinding room 21, grinding medium beads 28 are stored with a prescribed density therein, several lines of slits 29 for separating the treated slurry after treatment and the grinding medium beads 28 are formed on the central circumferential part and a cooling jacket 35 is formed inside the outermost wall 34.