An exposure control unit 15 controls a charge accumulation time for a CMOS sensor 10. The CMOS sensor 10 captures an image P1 with a charge accumulation time T1 and an image P2 with a charge accumulation time T2. The charge accumulation time T1 does not cause a flicker in an image under a light source blinking at a first blink cycle. The charge accumulation time T2 is different from the charge accumulation time T1. A difference image generation unit 17 generates a difference image DP that emphasizes to show a difference in luminance of the images P1 and P2. A flicker detection unit 18 detects a flicker occurrence in the image P2 based on a difference in luminance between P1 and P2 appearing in the difference image DP.