In a .phi..sub.2 cycle steal mode, a clock signal is selected such that a time period during which a RAM is connected to a timing signal generator for display is extended and a time period during which the RAM is connected to a CPU is shortened accordingly, without changing an overall period. This clock signal is used to actuate a switching circuit for the RAM while a clock signal having unmodified duty ratio is applied to the CPU, a ROM and external circuits so that a display data readout period from the RAM is extended without affecting the CPU clock frequency and the operation of other circuits. During this readout period, a plurality of display address signals are applied to the RAM from the timing signal generator and a plurality of data derived from the RAM are sequentially loaded in a register which is then read out at a desired timing to enable the display of a plurality of characters in one CPU clock period.