One aspect of the present invention may include a heat pump system having a Peltier unit in an outdoor space and an outdoor heat exchange unit in the outdoor space. The Peltier unit has a Peltier element with a heat-absorbing portion and a heat-radiating portion, a first substrate in contact with the heat-absorbing portion, a second substrate in contact with the heat-radiating portion, a metal case and a resin case. The metal case covers the first substrate and forms a first flow path between itself and the first substrate. The first flow path is connected in a loop-like fashion to the outdoor heat exchange unit by an outdoor piping. The resin case covers the second substrate and forms a second flow path between itself and the second substrate. The second flow path is connected in a loop-like fashion to the indoor heat exchange unit by an indoor piping.