PURPOSE: To prevent the contamination and damage of a microwave introducing window and antenna by plasma and to allow the stable use over a long period of time by using a coaxial cable to introduce microwaves into the reaction chamber of the microwave plasma CVD device and connecting the conductor of the coaxial cable and a base body.

CONSTITUTION: The microwaves emitted from a microwave power source 1 propagates in a waveguide 2 and arrive at a mode converter 3 where the microwaves are converted to a TEM mode suitable for the coaxial cable and propagate in the coaxial cable 4, by which the microwaves are introduced into the reaction chamber 8 and are introduced through the antenna 10 into the reaction chamber 8. The plasma 12 is generated only around the periphery of the base body in this way. The microwave introducing window plasma CVD device of this invention introduces the microwave directly into the substrate by using the coaxial cable in such a manner and, therefore, the problems, such as contamination and damage of the microwave introducing window and antenna, do not arise. Thus the device is usable stably over a long period of time. Since the plasma is stabilized, the quality of the film is improved.