To provide a pressure measuring device capable of measuring a wide pressure range without combining a vacuum gauge.

When vacuum atmosphere pressure is to be measured by using a vacuum gauge V including a filament F, grid G and a collector C, an upper limit value Ifmax is provided on a filament current If and, in a low pressure range, pressure from an ionic current Ii flowing to the collector C is found by limiting the filament current If by the action of the ionization vacuum gauge so that an emission current Ie may be constant. In a high pressure range, temperature of the filament F is lowered from the low pressure range, Pirani vacuum gauge actuated, and pressure is found from the quantity of heat of the filament F deprived of by gas molecule. In high pressure range, the filament current If can be controlled to the constant current of the upper limit value Ifmax.