1. A microscope image processing device for processing an observation image comprising: an optical element switching unit which switchably arranges an arbitrary optical element on an optical path of fluorescence from among a plurality of types of optical elements that transmit an excitation beam for exciting a sample and fluorescence emitted from the sample; an image pick up device which picks up the observation image via the optical element arranged by the optical element switching unit; an optical element determination unit which determines a type of the optical element arranged by the optical element switching unit based on the observation image picked up by the image pick up device; an optical element information storage unit which stores information on the plurality of types of optical elements that transmit an excitation beam for exciting the sample and fluorescence emitted from the sample; an optical element identification unit which identifies the type of the optical element determined by the optical element determination unit by referring to the optical element information storage unit; a fluorescence dye information storage unit which stores information on a plurality of fluorescence dyes; a fluorescence dye recognition information input unit which inputs fluorescence dye recognition information for recognizing a fluorescence dye; a fluorescence dye identification unit which identifies the fluorescence dye whose fluorescence dye recognition information is input by the fluorescence dye recognition information input unit by referring to the fluorescence dye information storage unit; and a false color setting unit which sets a false color on the observation image picked up by the image pick up device based on the type of the optical element determined by the optical element determination unit and based on a fluorescence dye characteristic corresponding to the fluorescence dye identified by the fluorescence dye identification unit.