Kamen Rider: Season 1 Episode 1 - The Mysterious Spider Man (1971)
https://www.youtube.com/watch?v=49txelAN5uo&list=PLnY1FL_e1HO5R3PEsEmueC4jZG7Jf2a_1&index - from the TokuSHOUTsu YouTube channel (25 mins - 1080p - Eng. subtitles)

Synopsis:
Takeshi Hongo, a young scientist boasting of an IQ of 600 and a racing prodigy, is abducted and his body surgically remodeled by Shocker, an evil secret society plotting for global domination.

Directed by Koichi Takemoto.

Cast: Hiroshi Fujioka, Akiji Kobayashi & Chieko Morikawa.

Trivia:
The original series spawned television and film sequels and launched the Second Kaiju Boom (also known as the Henshin Boom) on Japanese television during the early 1970s, impacting the superhero and action-adventure genres in Japan.

IMDb link
Wikipedia article (for entire series)

Some additional information about TokuSHOUTsu:
TokuSHOUTsu™ is dedicated to all things tokusatsu, featuring TV shows and live-action films with eye-popping special effects, vicious monster brawls, superhero stunts and spectacular sci-fi. The TokuSHOUTsu channel streams on Pluto TV, with select titles also available on demand at Shout! Factory TV.