Semiconductor logic integrated circuit device having first and second operation modes for testing

A semiconductor logic integrated circuit device comprising a signal selection means and a storing means, which is capable of adjusting the logic levels of an output signal therefrom. With such a circuit device, the signal selection means and the storing means are controlled in normal operation mode so that a parallel input signal is allowed to be output as a parallel output signal from output terminals of the circuit device after subjecting the parallel input signal to logical signal processing. On the other hand, the signal selection means and the storing means are controlled in a testing opertion mode so that the parallel input signal are output in serial mode from a serial signal output terminal of the circuit device, and a serial input signal to the signal selection means is allowed to be stored in the storing means to adjust the logic levels of the output signal from the circuit device at desired levels voluntarily.