Amid a flurry of social media excitement, Niantic Labs, the software company behind the game, announced it was "finally broadcasting" in Japan.
First released in the US, Australia and New Zealand on 6 July and now available in more than 30 countries, the game has been a global phenomenon.
The Japanese launch comes with a McDonalds sponsorship deal.
Fast food restaurants were expected to be advertised as places where people were guaranteed to find Pokemon, or as "gyms" where players can train up their captured monsters for virtual fights.
But a McDonald's spokesman said restaurants would "call on players not to become a bother to customers who are eating".
On Friday morning, excited Japanese fans began tweeting that they had been able to start playing.
"The moment I found out the servers were up I jumped right out of bed, got dressed and ran outside with my iPhone and two extra battery packs," Samuel Lucas, an Australian YouTuber based in Japan told the BBC.
"So far I've been to the Japan post office which was my first poke stop, and now I'm on my way to a big park near my house."
Other Pokemon Go users didn't have to look far, with 21-year-old fan Tomoharu Kudo finding a Charmander in his bed.
However, he soon ventured out in search of more Pokemon.
"I left my house to seek a new journey that will change my life," said Mr Kudo.
After weeks of stories about people in other countries running into trouble playing the game, Japanese authorities have taken precautions and issued a nine-point safety guide, in cartoon form.
The warnings, by the National Centre of Incident Readiness and Strategy for Cybersecurity, included asking users to register with "cool names that are different from real names" and cautioning them against heatstroke as they walk around in the sun.
"I want people to abide by the warning so that people can play it on smartphones safely," said Chief Cabinet Secretary Yoshihide Suga on Thursday.
Pokemon Go is an augmented reality game on smartphones which already has millions of people worldwide obsessively capture small creatures in public spaces.
It works by showing you a picture of your real surroundings as caught by the phone's camera on your screen, then uses GPS to place virtual little monsters within that picture on your screen.
The mix of virtual and real worlds allows players to, for instance, fight a dragon circling Big Ben or chase a spaceship moving down their street.
The monsters in it were first popular in the 1990s when they started on the Nintendo Game Boy. Back then, trading cards were a huge hit in school playgrounds and the new game manages to build on that legacy.