This is Giant Superman 22, published by Mimosa (SA Magazine Co) +/- 1963-1964.
It reprints the cover and this story from DC Comics' Action Comics 297 (1963):
"The Man who discovered Superman's Identity"
Also reprinted is this story from DC Comics' Action Comics 296 (1963):
Supergirl: "The Girl who was Supergirl's Double"
Also reprinted are these two stories from DC Comics' Adventure Comics 251 (1958):
"Superboy's Last Day"
Green Arrow: "The Case of the Super-Arrows"
48pages, glossy colour cover, black and white newsprint interior.
Here is the cover of issue 22 and DC Comics' original cover: