The present invention provides an image coding apparatus and its motion vector detection method, which can reduce a system cost also when the throughput of image data is increased. The image coding apparatus of the present invention comprises a search range frame memory 40 for outputting a search range for motion vector detection, a coding target frame memory 50 for outputting a coding target block, and a motion compensation unit 210 for performing motion compensation by using the coding target block which is input from the coding target frame memory 50 via a second data bus and the search range for the motion vector detection, which is input from the search range frame memory 40 via a first data bus, and obtaining a candidate block having a highest correlation with the coding target block in the search range.