To provide a screw which can be threaded even into an object to be screwed consist of magnesium or magnesium alloy which tapping the object for itself without producing chips and has large holding power, and provide a manufacture method thereof.

By grooving a shaft part of a blank beforehand, a, recessed parts 8 corresponding to thread ridge 5 of a screw 1 manufactured by rolling work are formed. The top of the thread ridge 5 sinks, as compared with the other part in these recessed parts 8. An angle of the thread ridge 5 is preferably set to 30 degees or less. By decreasing contact with an object to be screwed, even when it is constituted of magnesium or magnesium alloy, a small initial torque is generated at screw-in time, so that proper tightening can be performed and chips can be prevented from being produced.