Tokyo Metro Co. has started playing classical and "healing" background music inside some of its trains on the Hibiya Line on a trial basis after it accidentally played music last July and received positive responses from passengers.

The subway operator said Monday it is the first attempt to play background music on commuter trains in Japan and the company is eyeing full introduction of the service after taking passengers' reactions into consideration.

"We'd like to provide a comfortable environment inside trains," a Tokyo Metro official said.

The trial is being conducted on 13000-series trains introduced last March on the Hibiya Line that are equipped with a high-quality speaker system.

Six music pieces, including Frederic Chopin's Nocturnes, are being played during the daytime, with the volume level set slightly lower than that of train announcements.

"It doesn't bother me with this volume level. I think it's good passengers can enjoy soothing music as we can't have any view underground," a 37-year-old female passenger said.