A safety binding device for binding a boot on an alpine ski including a releasable retaining mechanism of the mechanical, hydraulic, viscoelastic type, which actuate a release as a function of the forces to which the boot is subjected and as a function of the duration Δt of the application of such forces. The release action occurs as soon as the magnitude of the force is greater than an actual release threshold, Sr, which is dependent upon the duration Δt of the application of force, such that if duration is greater than one second, the actual release threshold is between 50% and 75% of the theoretical release threshold, St, whereby: Δt>1 s; 0.75×St≧Sr(Δt)≧0.5×St, with the theoretical release threshold St being determined as a function of the skier's parameters in conformance with ISO standards. In a particular embodiment, the release principle, which defines the actual release threshold as a function of the duration, Sr (Δt), is of the exponential decrease type: Sr(Δt)=a+exp[(b−Δt) / c]; whereby a, b, and c are parameters.