In measuring frequency, an indirect method have usually been taken. In this method, there are two ways ordinarily, one is by applying the principle of mechanical or electrical resonance and another by applying variation of reactance due to transition of frequency. However, it goes without saying that frequency can also be measured by a direct method in Which there are two ways too. Namely, according to the definition of frequency:
Frequency=a number of cycles/time taken to complete the cycles of the numerator
Therefore, in direct measurement of frequency, the following two ways are employed:
1) To count the number of cycles in a certain time.
2) To measure the time in a given number of cycles. Comparing each of the above two in the point of accuracy and measuring time, it is believed that the former is more advantageous in measuring high frequency but disadvantageous in measuring frequency and the latter is just contrary. Generally, electronic frequency measuring devices familier to us employ the Item 1) and the devices employed the Item 2) have never been seen.
Given in this paper is the "Frequency Measuring Device" which employs the above mentioned Item 2). Experimental data are also given with the description that this kind of frequency measuring device can easily obtain high accuracy especially in measuring low frequency.