PURPOSE: To accomplish accurate calibration, by arranging a constant capacity container with a relatively large capacity and a variable capacity container, slender with a relatively small capacity.

CONSTITUTION: A variable capacity container 1 and a constant capacity container 4 are made to communicate with each other by a lure taper insertion and moreover, the connection 5 of the constant capacity container 4 is connected to a pressure transducer 8 through a three-way clock 7. Then, with the operation of the three-way cock 7, the constant capacity container 7 is opened to the atmosphere to make the communication space of an apparatus for pressure calibration equal the atmospheric pressure. Then, with the operation of the three-way cock 7 again, the communication space is shut down from the atmosphere to make the pressure transducer 8 communicate with the pressure calibration apparatus. Then, as a plunger 2 is advanced, a pressure is generated according to a reduction in the capacity of the communication space and the value of the pressure currently generated is compared with the value of the pressure indicated or recorded with the pressure transducer 8 to accomplish the calibration of an actually measured pressure.