To prevent damages of maintenance components of an engine by replacing at optimal maintenance replacement timing suited to a use fuel, when a specified fuel such as heavy oils is used.

A maintenance replacement timing control device includes a replacement timing setting means 16 for setting the replacement timing of maintenance components, a fuel concentration meter 14 for measuring concentration of fuels, and a replacement timing advancing means 17 for deciding that the use fuel is other than the specified fuel, if converting measured concentration into reference temperature, the reference temperature conversion concentration exceeds a threshold value. When the use fuel is other than the specified fuel, earlier replacements of the maintenance components can be achieved by advancing the maintenance replacement timing.