The fibre-optical strain gauge comprises a mechanical construction (1) providing a strain-dependent relative movement of oppositely positioned, spaced apart first and second optical fibre ends in a direction substantially perpendicular to the axial direction of the optical fibres (7a, 7b) and uses the varying transmission of light between the two fibres (7a, 7b) as an indication of the strain. The mechanical construction comprises fibre-holding elements (6a, 6b) for securing the two fibres (7a, 7b) to the mechanical construction (1) in an aligned relationship in the unstrained condition. The mechanical construction (1) further comprises: a) anchorage means (3a, 3b) for providing two substantially pointy-formed connections between the mechanical construction (1) and the object to be measured on, a line (8) through said two connection points (3a, 3b) defining a strain-measuring direction; b) two connecting rods (2a, 2b), comprising articulated connections at both ends, to the respective anchorage means (3a, 3b) at one end and to respective further parts (5a-5d) of the mechanical construction at the other end, respectively, said two rods (2a, 2b) extending substantially in the strain-measuring direction (8); c) a transmission construction, connected articulated to the rod (2a, 2b) ends opposite the respective anchorage means (3a, 3b), for transferring the movement of said rods (2a, 2b) in said strain-measuring direction (8) to the fibre-holding elements (6a, 6b) and for guiding the movement of said fibre-holding elements (6a, 6b) in a direction substantially perpendicular to said axial direction of said optical fibres (7a, 7b). By this construction it is possible to obtein strain gauge measurments which are substantially not influenced by movements of the measuring points in a plane perpendicular to the desired strain measuring direction.