PROBLEM TO BE SOLVED: To provide a granule processing apparatus which is excellent in performance of enclosing a granule material and a granule product so that they do not leak from the inside of the granule processing apparatus to an outside environment.SOLUTION: A coating apparatus includes: a rotary drum 1 which stores granules to be processed and is rotationally driven around its axis a casing 2 which stores the rotary drum 1 and an air supply chamber 3 which is installed on one end side of the casing 2 and communicates with the inside of the rotary drum 1 through an opening 1a on one end side of the rotary drum 1. Pressures inside the casing 1, the rotary drum 1, and the air supply chamber 3 are controlled so as to be lower than the pressure of the outside environment. When the pressure inside the casing 2 is designated as Pa, the pressure inside the rotary drum 1 is designated as Pb, and the pressure inside the air supply chamber 3 is designated as Pc, these pressures have a relation of Pb≤Pc
