To provide a frame rate conversion method capable of improving deterioration in visibility of an image because of a drop frame in the image when a frame rate is decreased.

In the case of decreasing the frame rate when a rate control section 103 detects that an image coding bit quantity reaches a specified value or over, the method allows a correlation value processing section 304 to output thinned image information on the basis of an image correlation value outputted from an encoder core part 302, a thinning determination section 308 determines a thinned image on the basis of thinned image information, thins frames and thereafter the method equalizes time information attached to data after being multiplexed by a time information adjustment section 309 at an interval equal to or more than the thinned interval. Thus, the method prevents the image from causing a drop frame and realizes that the image is not hard to see.