The invention is a device for sampling fluids under pressure from a well which comprises a chamber for retaining the fluid within a sample chamber (01). The chambers includes a first piston which allows or prevents fluid inflow into the lower part of the chamber. The first piston is displaced by means comprising an elastic element (20) disposed in a chamber filled with oil and connected to the piston by a rod (04). Sampled fluid transfer means allows control of the descent of a second piston (02) from the upper part to the lower part of the chamber so that the fluid remains at constant pressure in chamber during the transfer.