To provide an engine cleaning device 60 for cleaning components of an engine 20, in which damage to a component 50 to be cleaned is suppressed or prevented, and radical is supplied to the component 50 to be cleaned for cleaning the component 50 to be cleaned.

The engine cleaning device includes: a hydrogen peroxide supplier 75 for supplying hydrogen peroxide to gas in an upstream passage 46 through which gas heading for the component to be cleaned 50 flows; and a decomposer 65 for decomposing, near the component 50 to be cleaned in the upstream passage 46, the hydrogen peroxide supplied by the hydrogen peroxide supplier 75 into OH radical.