PURPOSE: To realize a self-service unloading by a method wherein, when oil is supplied from a tank lorry to an underground oil tank, a receiving amount of oil is calculated based on remaining amounts before and after the oil feeding to the underground oil tank, and date and time of receipt, amount of receipt and the like are recorded.

CONSTITUTION: Liquid level in an underground tank is surveyed by a liquid level sensor 4 from a start of oil feeding from a tank lorry to the underground tank, and an output from the sensor 4 is inputted into a level-amount changing circuit 55. The level-amount changing circuit 55 obtains an amount from the liquid level and inputs it into an operation circuit 56. The operation circuit 56 operates a receiving amount of oil according to a prescribed order from amounts of oil remaining in the tank before and after the receipt of oil. The receiving amount now operated is indicated to an outdoor indicator 6 through an outdoor indicator control circuit 59, and at the same time, a printer 58 is driven by a printer control circuit 57 to print out date and time of the oil receipt, amount of received oil and the like.