An endoscope system includes a light source apparatus (11) for emitting narrow band light (Gn, Vn) of green and violet in field sequential lighting, for endoscopic imaging. An image sensor (28) has plural pixels (80) arranged on an imaging surface, for imaging an object in a body cavity illuminated with the narrow band light, to output a pixel signal (P1i, P2i, Q1i, Q2i). The plural pixels include first and second pixels. The first pixel has a lower spectral sensitivity than the second pixel. A gain corrector (60) is supplied with the pixel signal by the image sensor, for performing gain correction of multiplying the pixel signal of the first pixel by a gain value (K1i, K2i), so as to compensate for a difference in the spectral sensitivity of the first pixel from the second pixel. Also, a noise reduction device performs noise reduction of the pixel signal after the gain correction according to the gain value.
