A bit assignment estimating device that accurately estimates bit assignment of a payload with fewer division patterns is provided. The bit assignment estimating device: divides a payload of received communication data to generate a plurality of blocks; estimates bit assignment of a block to be a certain value type; concatenates a block, which is adjacent to either of a block or a concatenation block which is estimated to be the continuous value type at a higher-order bit side, to the block or the concatenation block which is estimated to be the continuous value type when the block adjacent is estimated to be the status value type or the continuous value type; estimates whether the concatenation block is the continuous value type or not; and separates an immediately-close-concatenated block from a corresponding concatenation block when the concatenation block is estimated not to be the continuous value type.