PURPOSE: To reduce the number of control items, to allow the means acquiring necessary data and to make the size small by varying a reception range of an analog image signal and a period of receiving data by one picture element so as to receive data of an optional range as image data when the analog image signal is received as a digital signal.

CONSTITUTION: A means 12 receives part of an image signal representing a forward road state obtained by an image pickup means 11 as image data. A processing means 13 applies recognition processing to a forward drive environment at least from the data. A reception range setting means 15 sets which range of the data obtained by the means 11 is to be received as image data based on a detection result of a drive state such as a velocity of its own vehicle and a steering amount by a detection means 14 and a processing result from the means 13. A start time setting means 16 decides where the reception of image data is to be started with respect to each of scanning line data within the set range. Furthermore, a means 17 decides a period to receive one picture element of the image data from the range set by the means 15. Thus, the received period is made variable to receive the data of an optional range as image data, then the means is made small and simplified considerably and the means is mounted easily on a vehicle.