PURPOSE: To process the outline of an image smoothly without causing an increase in cost.

CONSTITUTION: After a 1st mode wherein a converted image signal of one frame consisting of two 1st fields is outputted by deciding the fields of the input image signal of frame constitution consisting of 1st and 2nd fields, writing the 1st field of the input image in a 1st field memory 2 for a 1st specific frame period in response to the decision, and reading the 1st stored field twice successively and a 2nd mode wherein a converted image signal of one frame consisting of two 2nd fields is outputted by writing the 2nd field of the input image signal in a 2nd field memory 4 for a 2nd specific frame period following the 1st specific frame period and reading the 2nd stored field twice successively are repeated at a specific ratio, a converted image signal of one frame read out of those 1st field memory 2 and 2nd field memory 4 twice successively is compressed.