To provide a mill which is simple in installation and short in installation period, and its installation method.

A crusher body 10 for crushing raw materials, a reduction gear 8 for reducing the rotational speed of the crusher body 10, and a plurality of crushers 2 having a lower housing 9 for storing the reduction gear 8 are juxtaposed and installed. An installation method of the crushers 2 comprises a step of installing rails 26 over an area for juxtaposing the crushers 2 of a floor on which the plurality of crushers 2 are installed, a step of assembling the reduction gear 8, the lower housing 9, and the crusher body 14 on a reduction gear integrated base 33 outside the floor, and a step of conveying the assembled crushers 2 one by one on the rails 26 by a truck 25, and installing them, and leaving the rails 26 behind on the floor.