1. An image coding apparatus comprising: a division unit configured to divide an input image into a processing target block; a prediction mode determination unit configured, in units of the processing target block divided by the division unit, to determine a mode of an intra-picture prediction of the processing target block; a holding unit configured to hold the intra prediction mode determined by the prediction mode determination unit; a prediction mode estimation unit configured to estimate the intra prediction mode of the processing target block based on an intra prediction mode of a surrounding block around the processing target block, which is held by the holding unit; a determination unit configured to determine whether the result of the prediction mode determination unit and the result of the prediction mode estimation unit match each other; a coding unit configured to code the result of the determination unit, and further, when the result of the determination unit indicates a mismatch, to code the result of the prediction mode determination unit; a mode comparison unit configured to acquire an intra prediction mode of one or more predetermined block surrounding the processing target block from the holding unit to compare the mode; and a control unit configured to control the coding unit based on the result of the mode comparison unit.