PURPOSE: To provide a screw fastening tool having a high workability, by which an extremely small screw or an extremely small nut in glasses can be reliably fastened.

CONSTITUTION: A plurality of screw fastening bits 2, 3, 4 are radially fixed or so implanted as to be replaced on the outer peripheral surface of a tool main body 1 formed into a ring shape. Thereby, the tool can be stably held because the tool main body 1 is formed into a ring shape, and the fastening precision is stabilized, and the workability becomes favorable, and work efficiency is improved. Moreover, the bit replacing-type screw fastening tool can easily comply with fastening of various kinds of screws or nuts by only replacing the bit by the required bit if various kinds of bits are prepared.