A two-reference-point-pair determining unit 101 determines two reference point pairs by selecting two transmission symbol points with their LLR computation target bit being 0 and two transmission symbol points with their LLR computation target bit being 1. An LLR computation unit 113 assigns weights to the two LLRs calculated for the two reference point pairs, respectively, followed by adding them, and further adds to the addition result a correction term that may be zero sometimes, thus computing LLR for the two reference point pairs.