To enable performing of a safe operation while maintaining classification performance by properly setting the amount of air to be blown into a device, and safe firing of biomass grinds without lowering the firing performance, even when the biomass grinds are burned by introducing them directly into a combustion device.

The biomass grinder 1 operates in the following way: biomass solid matter 100 supplied onto a grinding table 3 which is rotatably driven inside a cylindrical housing 2, is pressed and ground by a roller 5 that operates with the rotation of the table 3, and then the biomass grinds are transported upward by a blown-up air current generated by a primary air supplied from below the housing 2, and thereafter are classified into a coarse powder and fine powder. In addition, a throttling part which allows an air current path A for the blown-up air current to expand and contract, is arranged in the inner upper part of the housing 2, and the sectional area of the throttling part is set so as to allow the blown-up air current passing through the throttling part to fall within the range of a predetermined air tower velocity. The air tower velocity of the throttling part is preferably to be set within the range of 0.5 to 2.0 m/s.