Abstract: A swimmer's propulsion apparatus of the type comprising an anti-drift member and a propelling fish-tail member connected to the anti-drift member so as to perform a swinging motion with respect to said anti-drift member, wherein the improvement consists in that the propelling member is arranged to substantially freely pivot within a predetermined neutral sector about a pivot bar oscillated by the swimmer and that the rear portion of the propelling member beyond said pivot bar has a surface greater than its front portion.