PURPOSE: To position a workpiece exactly due to non-vibration and prolong the life of a tool by engaging and fixing jig pallets and jig cases and by engaging the workpiece in the state that it can be slidden in one way through a second engaging means.

CONSTITUTION: Jig pallets 14a and 14b for holding a workpiece and jig bases 12a and 12b for fitting it are arranged and fixed to each other through a first engaging means. And the workpiece is engaged in the state that it can be slidden in one way through a second engaging means. Then, the workpiece is not vibrated while being cut and also positioned exactly. A tool is, therefore, not damaged during cutting and can perform highly accurate machining. And the pallets 14a and 14b are free from the deformation caused by the heat generated during the cutting, and positioning accuracy can be maintained high for a long time. Highly accurate and economical machining process can, therefore, be carried out.