Abstract: A powdery and granular material treating apparatus wherein a powdery or granular material is contained in a rotary drum and the rotary drum is rotated about a horizontal axis to thereby coat the powdery or granular material. Ventilating perforations are formed on the entire surface or portions of the outer periphery of the rotary drum and drying air is fed to or exhausted from the rotary drum through these ventilating perforations. This powdery and granular material treating apparatus includes: seal plates for sealing drying air fed into the rotary drum; circular sliding frames provided on the sides of the outer periphery of the rotary drum, the outer surfaces of said sliding frames being in sliding contact with the seal plates at portions, through which air is fed to or exhausted from the rotary drum; and partition plates provided on the side of the outer periphery of the rotary drum at positions spaced apart in the circumferential direction of the rotary drum from one another.