The news comes days after Sony suggested the service will be in Japan by the end of December, after making its catalogue of tracks available via Recochoku, a distributor that is run by Japan's top labels.
Music Unlimited has launched today and will cost users 1,480 yen (circa $18.60) per month, but the company is offering an initial 30 day free trial.
Tim Schaaff, president of Sony Network Entertainment International said: "Bringing the cloud music subscription service to Japan, which is one of the largest music markets in the world, is a key step in the expansion of 'Music Unlimited,'"
Japan is now the seventeenth market where Music Unlimited is live. Previously, Sony fans in the company's native country could only buy songs from Sony online through other services, including iTunes, meaning Sony has to split the revenue with those providers.
The streaming services allows users to listen to tracks from a variety of devices, including: Android smartphones and tablets, the PlayStation3, PlayStation Vita, Sony's VAIO range, other Windows computers and Macs.