PURPOSE: To realize a high-accuracy pressure gauge, by enclosing the liquid free from air bubbles into a pressure gauge and then eliminating completely even the air bubbles remaining within the pressure gauge while securing a circulation of the liquid.

CONSTITUTION: A loop is formed between plural liquid enclosing ports such as the valves 5a, 5c, 5h, 5i or the like and the liquid storage tank 13 which supplies the enclosing liquid to the pressure gauge 1. Thus the liquid 12 is enclosed into the gauge 1 while securing a circulation of the enclosing liquid 12 into the loop by the electromagnetic pump 10 provided in the loop. And at the same time, the air bubbles in the liquid 12 are eliminated via the air bubble eliminating tank 8 which is installed at the position of the pressure gauge side and has the free liquid level with a vaccum drawn.