To solve the problem that it is impossible to perform highly accurate processing since a variation is easily caused in circularity of a through-hole of respective cylindrical bodies, due to performing processing by fixing an outer peripheral surface, when processing an inner diameter of a plurality of cylindrical bodies.

This inner diameter processing method provides the through-hole by polishing a prepared hole 1a by inserting a wire into the prepared hole 1a of the respective cylindrical bodies 1, by holding the plurality of cylindrical bodies 1 having the prepared hole 1a in the shaft direction by a fixture 3 so as to continue the respective prepared holes 1a. The method polishes and processes the prepared hole 1a, by rotating the plurality of cylindrical bodies 1 around a shaft, by rotating the fixture 3, by inserting the wire 2 into the respective prepared holes 1a, by connecting and fixing the plurality of cylindrical bodies 1 in the shaft direction in the fixture 3, by forming an end surface 1b contacting with the respective cylindrical bodies 1 as a rough surface. Thus, the through-hole small in a variation in high circularity can be formed, and manufacturing cost can be reduced.