The analog-to-digital converting circuit apparatus of the invention is intended to realize both low voltage operation and high speed operation of an analog-to-digital converting circuit without impairing the precision characteristic. In plural boosting circuits, voltages higher than each supply voltage are generated. These plural boosting circuits are controlled as the control timing is sequentially shifted by the controller. The boosted voltages delivered from the plural boosting circuits are accumulated in the capacitor, and supplied into the analog-to-digital converter. In the analog-to-digital converter, at the timing other than the changeover timing of the converting action of the analog-to-digital converter, the plural boosting circuits are changed over sequentially, and the boosted voltages are converted from analog to digital values.