To provide a city water meter testing device, capable of knowing the level of a start-up flow rate in a tested city water meter, and capable of precisely attaching a pilot detecting part for generating a pulse signal, in response to the rotation of a pilot, to an indication part of the tested city water meter.

This city water meter testing device for comparing the indication value of the tested city water meter with a water flow amount to detect metering precision of the tested city water meter is provided with a water supply part for making water flow in a testing pipe inserted with the tested city water meter; a reference flowmeter for measuring an instantaneous flow rate of the water in the testing pipe, the pilot detecting part for generating the pulse signal, in response to the rotation of the pilot; and a comparison determination part for counting the pulse signal obtained from the pilot detecting part to find a metered amount in the tested city water meter, and for comparing the metered amount with the water flow amount, found from an output of the reference flowmeter to calculate the metering precision in the tested city water meter.