Hiroshi Shiba is a car racer who is mortally wounded on a laboratory accident, but restored to life by his father, Professor Shiba, a talented scientist/archeologist. The Professor is investigating the relics of the ancient Yamatai Kingdom. He discovers a tiny bronze bell with sorcerous powers, and shortly afterwards he is murdered by the henchmen of Queen Himika, the ruler of the Yamatai, who wants to seize the ancient bell and its power.

Hiroshi learns about his father's death, and his legacy: after the accident, Hiroshi was transformed by his father into a cyborg, the bronze bell hidden in his own chest. With his newound power, he is able to transform into the head of a giant robot, the Steel Jeeg, created by Prof. Shiba with the purpose of stopping the Yamatai invasion of modern Japan. The minions of Queen Himika have huge haniwa robots, called clay phantoms buried thousands of years under Japan's soil, and only Jeeg can destroy them and save the world. Therefore, Hiroshi must roughly try to live his double life as his career as a racer who takes care of his mother and sister and a hero who fight to save the world.