Strip resonator for a mechanical watch movement, comprising a structure, an oscillating inertial element, and elastic strips forming a flat bearing for the inertial element, and a flat, anti-shock device arranged to protect each strip from rupture in the event of a shock, and including a first prestressed flexible element arranged to allow a variation in length during the expansion or contraction of a strip within a range of lengths corresponding to normal operation of this strip under the action of a stress of intensity lower than a first threshold, and to prevent the expansion or contraction of this strip when it is subjected to a tensile or respectively compressive stress of intensity higher than the first threshold, and the resonator includes, for the three-dimensional anti-shock protection of the strips, in an axial direction perpendicular to a main plane, axial protection means, which include, on the one hand, axial banking members for limiting the axial travel of at least one inertial element, and on the other hand, an axial anti-shock device comprising a second axially prestressed flexible element.