What is the 1970s Japanese tv show where a man turned into giant flying silver robot?

The 1970s Japanese TV show you're referring to is called "Ultraman". It's a tokusatsu superhero TV show that first aired in Japan in 1966 and it continued until 1980. The show featured the story of a giant alien from Nebula M78 who merges with a human host named Shin Hayata and transforms into the giant flying silver robot Ultraman to protect Earth.