1. An endoscope apparatus comprising: illumination means for irradiating at least three kinds of illumination light having different wavelengths including standard light, first reference light, and second reference light onto a biological object serving as a subject; illumination light switching means for periodically switching the at least three kinds of illumination light irradiated by the illumination means in each imaging frame; imaging means for receiving return light from the subject onto which the at least three kinds of illumination light switched by the illumination light switching means are irradiated and capturing image data in each imaging frame; and biological information acquisition means for acquiring biological function information relating to the biological object from the captured image data captured by the imaging means, wherein the illumination light switching means switches an irradiation order of the at least three kinds of illumination light by the illumination means at least in order of the first reference light, the standard light, and the second reference light, the standard light is irradiated onto the biological object by the illumination means to acquire a standard image by the imaging means, and at least two kinds of illumination light including the first and second reference light other than the standard light is irradiated onto the biological object by the illumination means to acquire reference images by the imaging means, and the biological information acquisition means calculates the biological function information based on the standard image and the reference images acquired by the imaging means.