PURPOSE: To reduce the influence of external noises greatly by changing a voltage interface which starts a meter by a voltage and makes a logical voltage response by impedance variation into a current interface through a conversion adapter.

CONSTITUTION: When the meter is started, the start relay 21 of a meter start terminal equipment 2 is operated and a start voltage 26 is supplied to the meter start relay 9 of the conversion adapter 1. A start relay contact 8 is made and the electronic water meter 3 beings to output meter inspection data 28. The serial binary output meter inspection data satisfies the polarity logic of a mark signal 27, the meter inspection data 28, and a space signal 29. The logical voltage is supplied to the meter inspection data output driving relay 10 of the conversion adapter 1. For the mark signal 27, a driving relay contact 11 has break contact logic 30 on a driving repeating cable 6 and a relay contact 18 is still made. For the space signal 29, make contact logic 31 is obtained on the driving repeating cable 6 and the relay contact 18 is broken.