A former member of the male idol group KAT-TUN, Junnosuke Taguchi, has been arrested on suspicion of possessing marijuana.
Sources say the health ministry's narcotics control department searched Taguchi's residence based on a tip and found dried cannabis on Wednesday.
Officers took Taguchi, aged 33, into custody on the spot. They also arrested his girlfriend, 38-year-old former actress Rena Komine who was living with him, on the same charge.
Investigators are looking into how and where the suspects obtained the banned drug.