A reaction processor includes: a reaction processing vessel placing portion for placing a reaction processing vessel provided with a channel into which a sample is introduced; a temperature control system, which controls the temperature of the channel in order to heat the sample inside the channel; and a liquid feeding system, which controls the pressure inside the channel of the reaction processing vessel in order to move the sample inside the channel. The liquid feeding system maintains the pressure inside the channel to be higher than the atmospheric pressure in the surrounding of the reaction processing vessel, more preferably 1 atm or higher, during a reaction process of the sample.