An encoder that encodes a picture, the encoder comprising: a processor; and memory, wherein the processor includes: a block partition determiner configured to partition the picture into a plurality of blocks, using a set of block partition modes obtained by combining one or more block partition modes each of which defines a partition type, the picture being read from the memory; and an encoding unit configured to encode the plurality of blocks, wherein the set of block partition modes includes a first partition mode that defines a partition direction and a total number of partitions for partitioning a first block (44-1), and a second block partition mode that defines a partition direction and a total number of partitions for partitioning a second block (44-2) which is one of blocks (44-2, 44-3, 44-4) obtained after the first block (44-1) is partitioned, characterized in that when the total number of partitions of the first block partition mode is three, the second block (44-2) is a center block among the blocks (44-2, 44-3, 44-4) obtained after the first block (44-1) is partitioned, and the partition direction of the second block partition mode is same as the partition direction of the first block partition mode, the second block partition mode includes only a block partition mode indicating that the total number of partitions is three, and wherein the encoding unit is further configured to encode a parameter for identifying the second block partition mode, said parameter includes a first flag indicating whether a block is to be partitioned horizontally or vertically, and does not include a second flag indicating a total number of partitions into which the block is to be partitioned. a block partition determiner configured to partition the picture into a plurality of blocks, using a set of block partition modes obtained by combining one or more block partition modes each of which defines a partition type, the picture being read from the memory; and an encoding unit configured to encode the plurality of blocks, wherein the set of block partition modes includes a first partition mode that defines a partition direction and a total number of partitions for partitioning a first block (44-1), and a second block partition mode that defines a partition direction and a total number of partitions for partitioning a second block (44-2) which is one of blocks (44-2, 44-3, 44-4) obtained after the first block (44-1) is partitioned, characterized in that when the total number of partitions of the first block partition mode is three, the second block (44-2) is a center block among the blocks (44-2, 44-3, 44-4) obtained after the first block (44-1) is partitioned, and the partition direction of the second block partition mode is same as the partition direction of the first block partition mode, the second block partition mode includes only a block partition mode indicating that the total number of partitions is three, and wherein the encoding unit is further configured to encode a parameter for identifying the second block partition mode, said parameter includes a first flag indicating whether a block is to be partitioned horizontally or vertically, and does not include a second flag indicating a total number of partitions into which the block is to be partitioned. <EOS>