To provide a one-way or two-way linear motion clutch mechanism that is lockable in an arbitrary position and allows an increase in the locking force according to the load thereon.

This linear motion clutch mechanism comprises a freely rotatable multiple-thread screw shaft 15 with both ends journalled on a rigid frame, two opposite movable bearing housings 11A and 11B with incorporated internally threaded inner races adapted to thread on the screw shaft 15, and springs 16A and 16B for urging the movable bearing housings 11A and 11B toward or away from each other. Cams turnable in a direction perpendicular to the direction of the multiple-thread screw shaft 15 have pivots, so that the distance between the movable bearing housings 11A and 11B and a movable reference bearing housing 10 sandwiched therebetween, which bearing housings are all threaded on the same screw shaft 15, is shortened or lengthened to lock or unlock the movable reference bearing housing 10 in the direction of the multiple-thread screw shaft 15.