To provide a sensor unit in a measuring device in which the sensor can be replaced that calibration is not necessary after replacement of the sensor.

According to the present invention, a measuring device body 1 has a sensor 10, a true value retaining part 9 for retaining a true value corresponding to an output of this sensor 10, a sensor unit 7 for outputting the true value based on output data of this sensor inputted from the measuring device 1, a connection part 6 to which the sensor unit 7 is connected in capable of replacement, an analog-digital conversion part 4 for converting an analog signal based on the output of the sensor inputted from the sensor unit 7 to a digital signal, and a control part 2 for sending an output signal of this analog-digital conversion part 3 to the sensor unit 7 and outputting the true value obtained by accessing the true value retaining means 9 by this.