An average inductor valley current mode voltage control device for a DC/DC converter comprises a sample-hold inductor valley voltage unit receiving at least two inductor valley currents of at least two consecutive cycles produced by the inductor and then converting the at least two inductor valley currents into an average inductor valley voltage; and a reference voltage generation unit connected to the sample-hold inductor valley voltage unit and a transistor switch of the DC/DC converter and receiving a voltage two times of an external voltage corresponding to two times of an average inductor current produced by the inductor, wherein a reference voltage is generated by subtracting the average inductor valley voltage from the voltage two times of the external voltage for control of the switching of the transistor switch of the DC/DC converter while a peak inductor current is stabilized at a designated value.