A method of coding image data into a bitstream, the method comprising: coding, in the bitstream, a split flag for indicating whether a region of a largest coding unit is divided into smaller regions, and data for indicating a prediction mode value indicating whether an inter prediction or an intra prediction is used for a target coding unit and for indicating a partition mode indicating whether the target coding unit contains one prediction unit or is divided into more than one prediction units (1101, 1103); and when the target coding unit is not divided into smaller regions, the intra prediction is used for the target coding unit, and the target coding unit is divided into a plurality of prediction units: arithmetically coding flags, each of which being for a different one of the plurality of prediction units in the target coding unit, to form a block of adjacent coded data in the bitstream, the flag indicating whether a most probable mode or a remaining mode is used for an intra prediction of a prediction unit (1104, 1201); bypass coding information, each piece of which being for a different one of the plurality of prediction units in the target coding unit, to form another block of adjacent coded data in the bitstream, each piece of the information indicating a most probable mode index value or a remaining mode value used to code the prediction unit (1106, 1202); and coding the target coding unit into the bitstream using the intra prediction modes of the plurality of prediction units as indicated by the flags and the information, wherein, in the bitstream, the another block of bypass coded information is located posterior to the block of arithmetically coded flags. coding, in the bitstream, a split flag for indicating whether a region of a largest coding unit is divided into smaller regions, and data for indicating a prediction mode value indicating whether an inter prediction or an intra prediction is used for a target coding unit and for indicating a partition mode indicating whether the target coding unit contains one prediction unit or is divided into more than one prediction units (1101, 1103); and when the target coding unit is not divided into smaller regions, the intra prediction is used for the target coding unit, and the target coding unit is divided into a plurality of prediction units: arithmetically coding flags, each of which being for a different one of the plurality of prediction units in the target coding unit, to form a block of adjacent coded data in the bitstream, the flag indicating whether a most probable mode or a remaining mode is used for an intra prediction of a prediction unit (1104, 1201); bypass coding information, each piece of which being for a different one of the plurality of prediction units in the target coding unit, to form another block of adjacent coded data in the bitstream, each piece of the information indicating a most probable mode index value or a remaining mode value used to code the prediction unit (1106, 1202); and coding the target coding unit into the bitstream using the intra prediction modes of the plurality of prediction units as indicated by the flags and the information, wherein, in the bitstream, the another block of bypass coded information is located posterior to the block of arithmetically coded flags. arithmetically coding flags, each of which being for a different one of the plurality of prediction units in the target coding unit, to form a block of adjacent coded data in the bitstream, the flag indicating whether a most probable mode or a remaining mode is used for an intra prediction of a prediction unit (1104, 1201); bypass coding information, each piece of which being for a different one of the plurality of prediction units in the target coding unit, to form another block of adjacent coded data in the bitstream, each piece of the information indicating a most probable mode index value or a remaining mode value used to code the prediction unit (1106, 1202); and coding the target coding unit into the bitstream using the intra prediction modes of the plurality of prediction units as indicated by the flags and the information, wherein, in the bitstream, the another block of bypass coded information is located posterior to the block of arithmetically coded flags.