An image processing apparatus which calculates a code amount obtained upon coding a coding block being obtained by dividing an image to be processed, determines an assigned code amount to be assigned to each of the coding blocks, based on a reference code amount and the code amount calculated for each of coding blocks in a coding group including a plurality of coding blocks, and generates coded data by coding each of the coding blocks using the assigned code amount as a target code amount, wherein the assigned code amount is determined so that a total of the assigned code amounts of the coding blocks in the coding group is the same among a plurality of coding groups, and fixed-length coding is carried out on a coding group-by-coding group basis by coding using the determined assigned code amounts.