A heat exchanger has (i) a first passage (45) in which a first fluid flows, (ii) a heat storage body (41) that is thermally connected to the first passage (45) and stores a warm heat or a cold heat, and (iii) a second passage (46) that is thermally connected to both of the first passage (45) and the heat storage body (41), the second passage in which a second fluid flows. The heat exchanger performs a heat exchange between the first fluid and the second fluid. The heat storage body (41) changes to a first phase in a solid state when a temperature of the heat storage body (41) is lower than or equal to a phase transition temperature, and changes to a second phase in a solid state when the temperature of the heat storage body (41) exceeds the phase transition temperature. The heat storage body (41) stores or dissipates heat depending on a phase transition between the first phase and the second phase. The second passage (46) is formed in the heat storage body (41) integrally with the heat storage body.