An image decoding method of decoding a bitstream to generate a decoded block, the image decoding method comprising: obtaining (S10001) quantized coefficients and first flag information that indicates whether or not an offset process is required, by performing variable-length decoding on the bitstream; obtaining (S10002) a decoded residual block by performing inverse quantization and inverse transform on the quantized coefficients; generating (S10003) a predicted block by predicting the decoded block; generating (S10004) a temporary decoded block by adding the decoded residual block to the predicted block; and generating (S10005 - S10007) the decoded block by executing, on the temporary decoded block, the offset process for correcting an error that is included in the temporary decoded block, when the first flag information indicates that the offset process is required; wherein the offset process is executed to add an offset value obtained from the bitstream to a value of a pixel included in the temporary decoded block; wherein the step (S10001) of obtaining quantized coefficients and first flag information further obtains unit-of-offsetting information indicating whether or not, in an area A including a plurality of blocks, the same offset value is used for all the blocks; and in the step (S10005 - S10007) of generating the decoded block, the offset process is executed on the temporary decoded block according to the unit-of-offsetting information; wherein, when the unit-of-offsetting information indicates that the same offset value is used for all the blocks in the area A, a new offset value is obtained when the offset process is completed for all blocks of the area A. obtaining (S10001) quantized coefficients and first flag information that indicates whether or not an offset process is required, by performing variable-length decoding on the bitstream; obtaining (S10002) a decoded residual block by performing inverse quantization and inverse transform on the quantized coefficients; generating (S10003) a predicted block by predicting the decoded block; generating (S10004) a temporary decoded block by adding the decoded residual block to the predicted block; and generating (S10005 - S10007) the decoded block by executing, on the temporary decoded block, the offset process for correcting an error that is included in the temporary decoded block, when the first flag information indicates that the offset process is required; wherein the offset process is executed to add an offset value obtained from the bitstream to a value of a pixel included in the temporary decoded block; wherein the step (S10001) of obtaining quantized coefficients and first flag information further obtains unit-of-offsetting information indicating whether or not, in an area A including a plurality of blocks, the same offset value is used for all the blocks; and in the step (S10005 - S10007) of generating the decoded block, the offset process is executed on the temporary decoded block according to the unit-of-offsetting information; wherein, when the unit-of-offsetting information indicates that the same offset value is used for all the blocks in the area A, a new offset value is obtained when the offset process is completed for all blocks of the area A. <EOS>