An encoding circuit includes an allocator configured to allocate symbols among a plurality of symbols within a constellation of multilevel modulation and correspond to values of a plurality of bit strings, a converter configured to convert values of each of bit strings excluding a first bit string so that, as a region within the constellation is closer to the center of the constellation, the number of symbols allocated in the region is larger, a switch configured to switch between a first time period in which a first error correction code is inserted and a second time period in which the first error correction code is not inserted, and an insertor configured to generate the first error correction code from a second bit string in the second time period and inserts the first error correction code in two or more bit strings in the first time period according to the switching.