A nucleic acid amplification device which includes a flow channel for feeding a reaction solution containing a target nucleic acid includes: a nucleic acid amplification reaction portion that amplifies the target nucleic acid contained in the reaction solution; and a fed-solution retention portion that retains the reaction solution. The flow channel includes a first flow channel disposed in the nucleic acid amplification reaction portion and a second flow channel disposed in the fed-solution retention portion, and the reaction solution fed from the first flow channel is retained in the second flow channel.