The invention relates to an apparatus for drying bulk materials, which has a hopper-shaped bulk material container 29 with adjustable side walls 30, by which the container 29 can be adjusted to the amount of bulk material to be dried, by varying the volume of the container and the angle of inclination of the hopper. To dehumidify the drying air, a membrane dryer 12 is provided, which processes preferably the compressed air of a compressed-air system 10, which is previously cleaned by filter elements 13 and 14. The rate of flow of drying air can be adjusted by a throttle 16 to the fill level of the container 29. In this manner an apparatus for drying bulk materials is created which is compact and therefore flexible in its application. Through optimization of the rate of flow of the drying air this apparatus is also economical in its consumption of compressed air.