Single-chip micro-computer having a plurality of operation modes

Disclosed are a single-chip micro-computer optimized for an electronic memorandum book, an electronic dictionary or the like by suppressing the increase of the number of terminals, and an electronic apparatus having therein the single-chip micro-computer. The single-chip micro-computer has: a mode setting register for establishing a mode setting signal for either a first mode for outputting a memory address signal or a second mode for outputting an arithmetic operation output stored in an output register on the basis of a control signal from a micro instruction generation circuit; and a selection circuit for outputting either the memory address signal or the arithmetic operation output to address signal terminals on the basis of the mode setting signal.