NOVELTY - Substrate supplying device of a biogas plant comprising a biogas fermenter (5), comprises a raw material storage (1), an air mill with high rotational speed as raw material crusher, which is an air vortex- or air flow mill, a particle filter (3), a filter for exhaust air purification, a conveying device for conveying lumpy raw material, a feeding device for supplying air, a device for discharging particle-laden exhaust air from raw material crusher to the particle filter, and conveying device, which connects the solid discharge of the particle filter to a input device of the biogas fermenter.    USE - Used as a substrate supplying device of a biogas plant(claimed).    ADVANTAGE - The device is cost-efficient and allows the fermentation of substances that are difficult to ferment. The method exhibits increased biogas yield.    DETAILED DESCRIPTION - Substrate supplying device of a biogas plant comprising a biogas fermenter (5), comprises a raw material storage (1), an air mill with high rotational speed as raw material crusher, a particle filter (3), a filter for exhaust air purification, a conveying device for conveying lumpy raw material from raw material storage to the raw material crusher, a feeding device for supplying air into the raw material crusher, a device for discharging particle-laden exhaust air from the raw material crusher to the particle filter, and conveying device, which connects the solid discharge of the particle filter to a input device of the biogas fermenter. The raw material crusher is an air vortex- or air flow mill. An INDEPENDENT CLAIM is also included for supplying substrate to the biogas plant, comprising conveying the raw material from the raw material storage into the air vortex- or air flow mill, crushing the raw material to a particle size of 200-300 mu m, subsequently depositing crushed raw material in the particle filter, and introducing it into the biogas fermenter.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of the method for supplying substrate.    Raw material storage (1)    Ultra rotor (2)    Particle filter (3)    Biogas fermenter (5)    Cooler (6)