In a case where a partition mode in which luma signals are partitioned horizontally and vertically is set when an intra prediction of a picture signal is made in units of minimal coding blocks set in advance, an intra prediction unit is configured to make an intra prediction of a chroma signal in units of prediction blocks of the intra prediction of chroma signals within the minimal coding block set in accordance with a chroma format. A second bitstream constructing unit constructs a bitstream of information relating to a luma intra prediction mode of a prediction block of luma signals and information relating to a chroma intra prediction mode of a prediction block of chroma signals.