A heat exchanging device includes: a heat exchanger configured to perform heat exchange between first operating oil used in an engine and second operating oil used in a fluid transmitting device and an automatic transmission; and a heat exchanging amount decreasing unit configured to, when a temperature of the second operating oil is lower than a predetermined temperature at which it is allowed to engage a lock-up mechanism, decrease a flow amount of at least one of the first and second operating oil flowing in the heat exchanger as compared to a case in which the temperature of the second operating oil is not lower than the predetermined temperature.