A heat absorbing and radiating device includes a driving unit having communicable first fluid outlets and fourth fluid inlets, a heat-exchange unit communicating at an end with third fluid outlets of the driving unit and at another end with an inlet end of a liquid-gas confluence unit, which communicates at an outlet end with an inlet end of a liquid-gas separation chamber, while the latter communicates at an outlet end with one of two second fluid inlets of the driving unit. The driving unit is provided therein with reciprocatingly movable magnets to alternately push first and second fluids into the heat-exchange unit before them enter the fluid-gas confluence unit, so that hot air is finally released from the liquid-gas separation chamber. Since radiating fins and cooling fan are omitted, the device has reduced volume for use with a heat source in a small space, such as a CPU of a portable computer.