An operation processing apparatus adapted to perform a data conversion on input bits has a logic circuit adapted to perform a data conversion on input bits. The logic circuit includes selectors configured in a hierarchical layer structure and controlled by select signals corresponding to the input bits. Constant values input to selectors located in a bottom layer of the hierarchical structure are selected and transferred toward a top layer from one layer to another. A constant value is finally selected and output from the top layer. The data conversion process is controlled by a control unit such that a pre-charge phase and an evaluation phase are performed alternately. In the pre-charge phase, all input values to the selectors are set to be equal. In the evaluation phase, an output bit for given input bits is produced. The select signals are switched in the pre-charge phase.