PURPOSE: To exactly control the discharge amount of an improving material all the time regardless of the oscillation of a ship by a method in which the discharge amount of an improving material is calculated on the basis of measuring results of tank weight, and a deviation between signal from the arithmetic device and a target discharge amount signal is obtained.

CONSTITUTION: A controller for supply of an improving material consists of an improving material storage tank 3 set on a ship, a weight measurer 2 for the tank 3, a delivery means 40 for the improving material, a regulator 4 for discharge amount of the improving material, and controllers 9 and 10. In the controller 10, average value of varying amounts per unit time for signals from the measurer 2 is calculated for correcting the weight, and the delivery amount of the improving material is calculated from the corrected weight signal. A deviation between signal from the arithmetic device and a target discharge amount signal is obtained, and on the basis of the deviation signal, the controller 9 is operated. Control on the discharge amount of improving material can thus be exactly made regardless of the oscillating movement of the ship all the time.