PURPOSE: To form an insulating film having excellent quality and thickness by successively increasing the diameter of a gas blowoff hole from the central part to the peripheral part of the upper electrode and uniformizing the amt. of a plasma state gas ion.

CONSTITUTION: A parallel-plate electrode consisting of the upper electrode 8 and the lower electrode 7 which are opposed to each other is used in the plasma vapor phase growth device. Plural atmospheric gas blowoff holes 10 are arranged on the upper electrode 8 in the radial direction from the central part and faced with the lower electrode 7. The diameters of the atmospheric gas blowoff holes 10 are stepwise increased from a blowoff hole (a) at the central part of the upper electrode 8 to a blowoff hole (b) and a blowoff hole (c) situated on the periphery. Besides, a substrate 11 is placed on the lower electrode 7.