The invention relates to the instrument for fluid injection and the dilatation probe for implantation in body cavities, which solves the problem of even and safe dilation of the probe based on a fluid injection in a probe, which takes shape of a cylinder. The instrument (I) for injection of the fluid, most favorably distilled water, consists of the handle (30), with the filling valve (24) and the variable volume cylinder (22) attached to the cover (29). In the body of the handle (30), the relief-adjusting valve (PRV), intake valve (UV), which is connected to the trigger (36) over the piston (34) and the thrust valve (PV) are mounted. The cylindrical extension (1) is attached to the fore of the body of the handle (30), with the coupling (S), for attachment of the dilatation probe (50, 60) for body cavities implantation, attached to the free end of it.