PURPOSE: To assure rapid movement of nuts without noise or vibration by pressing each of nuts in the direction brought close to each other with an elastic material in those in which a block is slidably arranged along the outer circumferential face of two nuts screwed to a screw in the separated state.

CONSTITUTION: A screw driving mechanism has two nuts 22 (22-1, 22-2) which are screwed in a screw 21 in the separated state reciprocated by rotation of the screw 21 and has a block 23 arranged slidably along the outer circumferential faces 22-1a and 22-2a on the end side opposed to each of the nuts 22. And to this block 23, a first and a second holders 24 (24-1, 24-2) locked at each of the nuts 22 are fixed. In this case, each of the holders 24 presses the both nuts 22 in the direction brought close to each other by locking them at end faces 221b and 22-2b of the outside of the corresponding nut 22 through an elastic material 25-1 and 25-2 having rubber elasticity. Thus, rapid movement of the nuts 22 interlocked with high-speed rotation of a screw 11 can be secured.