In-line Fraunhofer holography is useful for measuring the size and spatial distribution of moving or stationary particles in air or a liquid from a few micron to a few hundred micron in diameter. However, the reconstruction processes of the measurement are tedious and take appreciable time, therefore the automatic measuring instrument is needed to have successful results. This paper deals with a fundamental study on the automatic holographic particulate measurements. The results obtained are as follows. (1) CCD line sensor-scanning device is built so that holographic reconstructed images can be stored to computer. (2) Using this device, light intensity distribution in the reconstructed image of wire is observed, and the results agree with theoretical simulations. (3) The index W-value is proposed as a focusing parameters. It is proved to be valid for determining the focal point of reconstructed real image. (4) The diameter and location of the wire can be measured automatically with this system.