1. A markup assistance apparatus comprising: an acquisition unit configured to acquire feature amount for respective tags, each of the tags being assigned to character strings included in a shared markup text, at least one of the tags being different from other tags, the feature amount being a value used to define a first similarity which indicates a degree of similarity between tags; a first calculation unit configured to calculate, for respective character strings, a dispersion of feature amounts of the tags; a detection unit configured to detect a first character string assigned with a first tag having the dispersion not less than a first threshold value as a first candidate including the first tag to be corrected; and an output unit configured to output the first candidate.