Abstract: A vapor deposition apparatus includes a plurality of gas sources, a first gas feed line which is in fluid communication with the gas sources and through which a gas necessary for conducting vapor deposition is introduced into a reaction pipe, a second gas feed line which is in fluid communication with the gas sources and through which a gas unnecessary for conducting vapor deposition is exhausted, a detector for detecting a difference A in pressure between the first and second gas feed lines, the detector being disposed upstream of inlet ports at which gases are supplied to the first and second gas feed lines from the gas sources, a calculator for calculating and storing a difference B in pressure between the first and second gas feed lines to be measured at a location at which the detector is disposed, which difference B in pressure would cause the difference A in pressure measured at the inlet ports to be reduced to within an allowable range, and a pressure regulator disposed on one of the first and second