An output buffer circuit comprising a pull-up transistor, a pull-down transistor coupled to the pull-up transistor, a first voltage source for supplying a driving voltage, a second voltage source for supplying a reference voltage, a device for comparing the driving voltage with the reference voltage, a driving voltage detector for producing a signal in response to operation of the comparing device, first and second pull-up driving buffers, the first and second pull-up driving buffers being activated according to the signal from the driving voltage detector, the pull-up transistor being driven by one of the pull-up driving buffers, and first and second pull-down driving buffers, the first and second pull-down driving buffers being activated according to the signal from the driving voltage detector, and the pull-down transistor being driven by one of the pull-down driving buffers.