irrespective of the body diode 83 referring to fig9 a symmetrical dc dc converter 85 according to a fifth embodiment of this invention has a structure in which the diode operation in the dc dc converter in fig8 is realized by synchronous rectification so as to improve the efficiency specifically in the fifth embodiment a diode 21 is connected to one end of each fet 81 through a resistor 87 so as to perform analog control in a manner such that the output of an operational amplifier 89 is not saturated on a minus side as described above according to the first through the fifth embodiments of this invention it is possible to provide a symmetrical dc dc converter operable in a desired energy transfer direction and at a desired step up or a desired step down ratio referring to fig1 a symmetrical dc dc converter 91 according to a sixth embodiment of this invention is used in a similar energy transfer system to that mentioned in conjunction with the second embodiment the converter 91 is connected to the electric double layer capacitor 17 a solar cell 93 and a light emitting device 95 as an energy storage device a power generator and a load among which.