A dental X-ray photographic system in the oral cavity comprises a photographing unit and an assist unit. The photographing unit has a receiver having an X-ray sensor. The assist unit has a base board and a supporter. The supporter is set at the end part of the base board. The end part of the base board is inserted in the oral cavity when X-ray photographic operation is performed. The supporter supports the receiver by clipping a salient portion of the receiver in a back face direction.
