A nucleic acid amplification device which includes a flow channel for feeding a reaction solution containing a target nucleic acid, the nucleic acid amplification device comprising: an introduction portion for introducing the reaction solution; a nucleic acid amplification reaction portion that is configured to amplify the target nucleic acid contained in the reaction solution by subjecting it to cyclic temperature changes; a fed-solution retention portion that is provided downstream of the nucleic acid amplification reaction portion and is configured to retain the reaction solution reacted in the nucleic acid amplification reaction portion; a heater for heating the reaction solution containing the target nucleic acid, the heater being disposed opposite to the nucleic acid amplification reaction portion and comprising a plurality of heater blocks (31, 32); and a discharge portion for discharging the reaction solution, wherein the flow channel has one end part connected to the introduction portion and the other end part connected to the discharge portion, wherein 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, wherein the second flow channel is configured to retain a fluid front part of the reaction solution fed from the first flow channel, wherein the nucleic acid amplification reaction portion includes at least two regions corresponding to separate heater blocks (31, 32) that are configured to be set at predetermined different temperatures, thus defining temperature zones which have different temperatures when the device is in use, wherein the first flow channel is formed to pass back and forth or cyclically through the at least two temperature zones, characterized in that the second flow channel has a volumetric capacity that is 30% or more of a total volumetric capacity of the flow channel, and in that the flow channel is configured so that the reaction solution may be fed and may advance through the flow channel by capillary force. an introduction portion for introducing the reaction solution; a nucleic acid amplification reaction portion that is configured to amplify the target nucleic acid contained in the reaction solution by subjecting it to cyclic temperature changes; a fed-solution retention portion that is provided downstream of the nucleic acid amplification reaction portion and is configured to retain the reaction solution reacted in the nucleic acid amplification reaction portion; a heater for heating the reaction solution containing the target nucleic acid, the heater being disposed opposite to the nucleic acid amplification reaction portion and comprising a plurality of heater blocks (31, 32); and a discharge portion for discharging the reaction solution, wherein the flow channel has one end part connected to the introduction portion and the other end part connected to the discharge portion, wherein 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, wherein the second flow channel is configured to retain a fluid front part of the reaction solution fed from the first flow channel, wherein the nucleic acid amplification reaction portion includes at least two regions corresponding to separate heater blocks (31, 32) that are configured to be set at predetermined different temperatures, thus defining temperature zones which have different temperatures when the device is in use, wherein the first flow channel is formed to pass back and forth or cyclically through the at least two temperature zones, characterized in that the second flow channel has a volumetric capacity that is 30% or more of a total volumetric capacity of the flow channel, and in that the flow channel is configured so that the reaction solution may be fed and may advance through the flow channel by capillary force.