In order to accurately measure a shape feature of a minute droplet arranged on a substrate by a simple method, with respect to the droplet, the substrate is perpendicularly irradiated with laser light to cause diffracted light fluxes generated during passage of the laser light through the droplet to interfere with each other, so that a diffraction pattern is obtained. The diffraction pattern formed on a screen of a detector as an image is picked up by an image pickup apparatus. The shape feature of the droplet is measured by using the resultant diffraction pattern and a refractive index of the droplet.