Reception unit receives data indicating water temperature of a body of water through which a vessel voyages, vessel speed, and a period for which those values are maintained. From storage unit, index value acquisition unit reads out a decrease amount of anti-fouling paint corresponding to the water temperature and vessel speed received by reception unit. Index value specification unit specifies a decrease amount of anti-fouling paint in the period by multiplying the length of time of the period received by reception unit by the decrease amount read out by index value acquisition unit. Remaining amount acquisition unit integrates the decrease amounts of the anti-fouling paint specified by index value specification unit at the time of coating with the anti-fouling paint and onward. Remaining amount specification unit specifies a current paint film thickness of the anti-fouling paint by subtracting the decrease amount of the anti-fouling paint integrated by remaining amount acquisition unit from the paint film thickness at the time of coating with the anti-fouling paint.