A pressure measurement system comprising: - a vacuum gauge including, inside a main body to be mounted on an object to be measured: a sensor section; a control section which supplies the sensor section with power, the control section controlling the working of the sensor section and also processing an input from the sensor section and outputting a predetermined signal; a power circuit section (40, 50) supplying the control section with power; the power circuit section (40, 50) receiving power supply from an external power source; and a switching section for switching the power supply to the control section through the power circuit section (40, 50), the switching section comprises switching elements (71a, 71b) and level shift circuits (72a, 72b), the switching section arranged such that, corresponding to the input voltage to the power circuit section (40, 50), the first and second switching elements (71a, 71b) are on-off controlled so as to switch over the power supply to the control section; and - a terminal device (Mt) connectable to the control section through a communication line of a communication circuit section in a manner to be freely communicated with the control section, and also capable of supplying the power circuit section with power in one of a wired manner and a wireless manner, characterized in that: - the vacuum gauge is arranged to judge the power supply from the terminal device (Mt) to the control section, such that: - in case power is supplied from both the external power source and the terminal device (Mt), if power supply from the external power source is confirmed to be in a range required for the normal operation of the sensor section, the control section is supplied with power from the external power source; - in case the power is being supplied only from the terminal device (Mt) but the rated voltage that is required for the normal operation of the sensor section is not being supplied, the power is supplied only to the control section, and the control section and the terminal device (Mt) are connected with each other through the communication line. - a vacuum gauge including, inside a main body to be mounted on an object to be measured: a sensor section; a control section which supplies the sensor section with power, the control section controlling the working of the sensor section and also processing an input from the sensor section and outputting a predetermined signal; a power circuit section (40, 50) supplying the control section with power; the power circuit section (40, 50) receiving power supply from an external power source; and a switching section for switching the power supply to the control section through the power circuit section (40, 50), the switching section comprises switching elements (71a, 71b) and level shift circuits (72a, 72b), the switching section arranged such that, corresponding to the input voltage to the power circuit section (40, 50), the first and second switching elements (71a, 71b) are on-off controlled so as to switch over the power supply to the control section; and - a terminal device (Mt) connectable to the control section through a communication line of a communication circuit section in a manner to be freely communicated with the control section, and also capable of supplying the power circuit section with power in one of a wired manner and a wireless manner, - the vacuum gauge is arranged to judge the power supply from the terminal device (Mt) to the control section, such that: - in case power is supplied from both the external power source and the terminal device (Mt), if power supply from the external power source is confirmed to be in a range required for the normal operation of the sensor section, the control section is supplied with power from the external power source; - in case the power is being supplied only from the terminal device (Mt) but the rated voltage that is required for the normal operation of the sensor section is not being supplied, the power is supplied only to the control section, and the control section and the terminal device (Mt) are connected with each other through the communication line. - in case power is supplied from both the external power source and the terminal device (Mt), if power supply from the external power source is confirmed to be in a range required for the normal operation of the sensor section, the control section is supplied with power from the external power source; - in case the power is being supplied only from the terminal device (Mt) but the rated voltage that is required for the normal operation of the sensor section is not being supplied, the power is supplied only to the control section, and the control section and the terminal device (Mt) are connected with each other through the communication line.