A heat treatment device configured with a first fluid that is a reaction fluid and a second fluid flowing therethrough, the device comprising: a heat exchange unit including a first flow channel through which the first fluid flows and a second flow channel through which the second fluid flows; and a heat transfer structure removably placed in the first flow channel, characterized in that the device further comprises: a first information acquisition unit connected to an outlet side of the first flow channel to acquire temperature information for specifying a temperature, and configured to cause comparison of the temperature information with a temperature of the first fluid, preset as a reference condition, after lapses of time; a second information acquisition unit connected to the outlet side of the first flow channel to acquire compositional information for specifying a composition of the first fluid after each lapse of time; and a control unit that is configured to confirm that the reference condition is fulfilled in accordance with the temperature information acquired by the first information acquisition unit, and to cause the second information acquisition unit to acquire the compositional information when the reference condition is fulfilled, and to calculate a reaction rate, or a yield, after each lapse of time in accordance with the composition specified according to the compositional information acquired by the second information acquisition unit, so as to estimate a service life of the heat transfer structure in accordance with the reaction rate, or the yield, wherein the heat transfer structure is a catalyst body. a heat exchange unit including a first flow channel through which the first fluid flows and a second flow channel through which the second fluid flows; and a heat transfer structure removably placed in the first flow channel, characterized in that the device further comprises: a first information acquisition unit connected to an outlet side of the first flow channel to acquire temperature information for specifying a temperature, and configured to cause comparison of the temperature information with a temperature of the first fluid, preset as a reference condition, after lapses of time; a second information acquisition unit connected to the outlet side of the first flow channel to acquire compositional information for specifying a composition of the first fluid after each lapse of time; and a control unit that is configured to confirm that the reference condition is fulfilled in accordance with the temperature information acquired by the first information acquisition unit, and to cause the second information acquisition unit to acquire the compositional information when the reference condition is fulfilled, and to calculate a reaction rate, or a yield, after each lapse of time in accordance with the composition specified according to the compositional information acquired by the second information acquisition unit, so as to estimate a service life of the heat transfer structure in accordance with the reaction rate, or the yield, wherein the heat transfer structure is a catalyst body. a first information acquisition unit connected to an outlet side of the first flow channel to acquire temperature information for specifying a temperature, and configured to cause comparison of the temperature information with a temperature of the first fluid, preset as a reference condition, after lapses of time; a second information acquisition unit connected to the outlet side of the first flow channel to acquire compositional information for specifying a composition of the first fluid after each lapse of time; and a control unit that is configured to confirm that the reference condition is fulfilled in accordance with the temperature information acquired by the first information acquisition unit, and to cause the second information acquisition unit to acquire the compositional information when the reference condition is fulfilled, and to calculate a reaction rate, or a yield, after each lapse of time in accordance with the composition specified according to the compositional information acquired by the second information acquisition unit, so as to estimate a service life of the heat transfer structure in accordance with the reaction rate, or the yield, wherein the heat transfer structure is a catalyst body.