To provide a friction disc device in oil to effectively utilize the characteristics of a carbon-carbon composite material disc at a favorable cost.

This friction device in oil comprises carbon-carbon composite material discs 30; and metal discs 10 and 20 arranged alternately with the composite material discs. The carbon-carbon composite material disc 30 is an elastic disc inserted between a rotor or a drive metal disc and a stator of a driven metal disc 20.