PURPOSE: To minimize a stack source and ease multiplexed levels by processing incorporated instructions in each incorporation level and releasing a stack means in every processing of one text incorporating information.

CONSTITUTION: Incorporating instructions INC1, INC2, INC3 in an input text a01 are successively processed to prepare an intermediate text obtained by incorporating external texts a11, a12 into the input text a01. At that time, incorporating instructions INC4, INC5, INC6 having a level "1" are left unprocessed. In the next stage, incorporating instructions INC4, INC5, INC6 in said intermediate text are processed to prepare a new intermediate text in which texts a21, a22, a23 having a level "2" are incorporated. Incorporating instructions INC7WINC10 in the new intermediate text are left unprocessed. By repeating said operation also in levels "3" and "4", the whole incorporation of texts is completed.