A narrow-band observation image (Pnb) and a spectral estimation image (SP) are automatically switched based on the type of a subject. In an endoscopic image (P) obtained by a scope (20), judgment is made as to whether the endoscopic image (P) was obtained by close-up imaging or by distant-view imaging. When it is judged that the endoscopic image (P) was obtained by distant-view imaging, white light (L1) is output from a light source unit (10) and a spectral estimation image (SP) is output. When it is judged that the endoscopic image (P) was obtained by close-up imaging, narrow-band light (L2) is output from the light source unit (10) and a narrow-band observation image (Pnb) that has been obtained when the narrow-band light (L2) was output is output.
