A novel contact area measuring apparatus is provided. The contact area measuring apparatus includes a light transmissive substrate 6 in contact with a specimen 7, illumination means for illuminating the light transmissive substrate 6 with white light from the opposite side of the light transmissive substrate 6 to the specimen 7, interference image acquisition means 11 for acquiring an interference image produced by the light reflected off the specimen 7 and the light reflected off the light transmissive substrate 6, intensity histogram creation means for creating an intensity histogram from information on the intensity of the interference image, and contact area computation means for calculating a contact area from the intensity histogram. The interference image acquisition means 11 acquires an interference image and information on the intensity of the interference image. The intensity histogram creation means forms separate RGB intensity information from the information on the intensity of the interference image and creates a G-intensity histogram. The contact area computation means separates the intensity histogram into a plurality of normal distributions by using optimized approximation of complex normal distribution and calculates the contact area from the lowest-intensity normal distribution.