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, and a second block partition mode that defines a partition direction and a total number of partitions for partitioning a second block which is one of blocks (44-2, 44-3, 44-4) obtained after the first block is partitioned, characterized in that when the total number of partitions of the first block partition mode is three, the second block is a center block among the blocks (44-2, 44-3, 44-4) obtained after the first block 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, and a second block partition mode that defines a partition direction and a total number of partitions for partitioning a second block which is one of blocks (44-2, 44-3, 44-4) obtained after the first block is partitioned, characterized in that when the total number of partitions of the first block partition mode is three, the second block is a center block among the blocks (44-2, 44-3, 44-4) obtained after the first block 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.