PURPOSE: To make it possible to obtain a desired resolution automatically by operating the frequency of a signal to be measured, based on the frequency division ratio of the signal to be measured and on the counted value of a pulse obtained while a gate is opened by a frequency-division pulse.

CONSTITUTION: A signal to be measured (a), having a frequency f1, is divided at the frequency division ratio N by a frequency dividing circuit 1 to control the opening of an AND gate 2. A reference signal (b) having a frequency f0 and passing through this gate 2 is counted by a counting circuit 4. A counted value thus obtained being taken as an address, a tble 3 storing a frequency division ratio corresponding to a set value of resolution is accessed and the required frequency division ratio N is set in the circuit 1. The reference signal via the gate 2 is counted in the same way by the circuit 4, and an operator 5 conducts an operation based on the formula according to the counted value K of the reference signal and the frequency division ratio N read from the table 3, whereby the frequency f1 is determined. In this case, the counted value K becomees large in accordance with the frequency division ratio N, the resolution is thereby improved, and thus a frequency counting circuit making it possible to obtain a desired resolution antomatically is attained.