PURPOSE: To permit the method of press fitting a column unit and its jig to be usefully applied for accurate assembly of a rotary unit, by constituting the method and the jig such that reaction resisting force can be released when the column unit advances being forced to be fitted by a distance almost 1/3 times the height in the axial direction.

CONSTITUTION: When a column unit 1 is forced to be fitted by pressure into a column- shaped hole 2 by using a press fit jig, an adapting member 4, enabled to slide moving for a column-shaped hole 3, is fitted and adapted to a bottom surface of the column unit 1. Next the column unit 1, when its press fitted process advances at a point of time with the unit 1 being fitted by a distance about 1/3 times the height (h) in the axial direction of the column unit 1, is released from reaction resisting force K, having been applied by a fluid pressure 9, by opening a discharge valve 93. The reason for releasing the reaction resisting force K at this point of time is that an accurate press fit attitude is established by completely aligning the center axial line of the column unit 1 to the center axial line of the hole 2 if the column unit 1 is fitted by a distance about 1/3 times the height in the axial direction of the column unit 1. In this way, the method and the jig are remarkably useful for accurate assembly of a rotary unit.