A method of coding image data into a bitstream, the method comprising: coding, in the bitstream, a split flag for indicating whether a coding unit is divided into smaller coding units, and data for indicating a prediction mode information 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 a plurality of prediction units (1101, 1103), wherein the partition mode is capable of being a 2Nx2N partition mode in which a coding unit contains one prediction unit; and when the target coding unit is not divided into smaller coding units, 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 data 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 data 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. coding, in the bitstream, a split flag for indicating whether a coding unit is divided into smaller coding units, and data for indicating a prediction mode information 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 a plurality of prediction units (1101, 1103), wherein the partition mode is capable of being a 2Nx2N partition mode in which a coding unit contains one prediction unit; and when the target coding unit is not divided into smaller coding units, 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 data 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 data 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. 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 data 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 data 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.