PURPOSE: To omit a bushing and to reduce the heat generation of a bearing part to eliminate the backlash of said bearing part, by a method wherein the shaft stem of a drive shaft is divided into a pluraity of parts in the circumferential direction and a plurality of spiral support surfaces are formed to a bearing.

CONSTITUTION: The shaft stem part 4a of a drive shaft 4 is formed so as to have four surfaces 4d each parallel with each side of a hole 4b having a square cross sectional shape and said surfaces 4d function as non-contact surface during rotation. Elongated split cylindrical surfaces 4c extending to the direction of the drive shaft 4 function as slide surfaces to be supported. In addition, four spiral grooves 1d are provided to a bearing surface and four spiral elongated surfaces 1c consitute slide support surfaces. Each spiral has a direction same to the rotary direction of the drive shaft and prevents oil from invading into the instrument.