PURPOSE: To reduce data quantity to be processed and to execute a number confirmation within a prescribed time by cutting out a plate frame within a limit range estimated.

CONSTITUTION: A digital picture signal having a number plate is differential- picture-processed by a differentiating circuit 15, binarized, scanned by a prescribed window, extracted as a window central value, divided into unit pictures by a compressing circuit 18, a maximum value is extracted and a picture compression is executed. A number plate position in a picture is estimated and the plate frame is cut out by a CPU 20 within the estimated range.