To uniformly supply and save the supply amount of reactive gas to a work by sharing a holding mechanism and a reactive gas supply and to hold the work without causing damage thereto during holding.

A work holding mechanism 1 has a holding part 2 for holding a work W, a supply part 4 for supplying reactive gas to the holding part and an encircling periphery 5 provided around the work W, the holding part 2 including a supply space 6 for supplied reactive gas and a supporting protrusion 3 located at a position of contacting the work W for forming a distribution passage P for the reactive gas and the encircling periphery 5 having the lower end 5a arranged under the lower face of the supported work, wherein an exhaust passage S for the reactive gas is formed a constant space from a moving path plane R of the work W.