To obviate the need for washing residual food and to facilitate the peeling of plastics from paper.

A food packaging material in which paper is coated with biodegradable plastics containing an aliphatic polyester as a main component and to which residual food adheres is supplied to a fermentation tank, the plastics and the residual food are decomposed by aerobic fermentation to be converted into compost. After that, residual paper left undecomposed is separated from the compost to be recovered.