A microscope apparatus that has an electronic image pickup device arranged on an image surface of an imaging optical system, a component for separating light from a light source into two portions, a device for changing a phase difference between the two portions of light, a device for storing information on the images picked up by the image pickup device, and information processor for processing the information of images. The images are picked up by the electronic image pickup device as the phase difference is changed, and the information on the images is multiplied by a periodic function, as a weight function, which is given the phase difference as variable, and a resultant product is integrated so that a differential interference microscope apparatus capable of accurately obtaining a phase distribution of the object or a phase-contrast microscope apparatus capable of effectively enhancing a resolving power without lowering an image contrast is obtained.