1. A markup assistance apparatus comprising: a processing circuitry coupled to a memory, the processing circuitry being configured to: acquire a 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 and wherein each of the tags is used to control a text-to-speech processing of the shared markup text; calculate, for respective character strings, a dispersion of feature amounts of the tags; 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 output the first candidate.