A thermal cycler (1) includes a holder (11) that holds a biotip (100) filled with a reaction mixture and liquid having a smaller specific gravity than the reaction mixture and being immiscible with the reaction mixture, the biotip (100) including a channel (110) in which the reaction mixture moves, a heating unit (12) that heats a first portion (111) of the channel when the biotip (100) is in the holder (11), and a driving unit (20) that disposes the holder (11) and the heating unit (12) by making a switch between a first disposition and a second disposition, the first disposition being such that the first portion (111) is in a lowest part of the channel (110) with respect to a gravitational force direction when the biotip (100) is in the holder (11), the second disposition being such that a second portion (112) that is a different portion from the first portion (111) relative to a moving direction of the reaction mixture is in the lowest part of the channel (110) with respect to the gravitational force direction when the biotip (100) is in the holder (11).