A door locking device for preventing a door from opening during a side collision comprises a base having one surface provided with an outside lever and another surface provided with a door latch to extend from the outside lever to contact an extending part which has a guide part extended through the base to be horizontal with the extending part. An inner side part of the guide part has a plurality of long grooves and a plurality of short grooves which are horizontal with the extending part. A rotator is inserted into the guide part and has a plurality of long ribs and a plurality of short ribs. A cap-shaped button has a bottom surface in contact with the plurality of long ribs. A blocking lever is linked to an upper end of the button and pivotably mounted in the base.