In order to save space and manufacturing costs a pull-off effect for the operation of a key should be achieved by using a single spring. Thus the spring must have an arc-like force vs. displacement characteristic having a maximum of force about on half-way of the key stroke. This is achieved by a meander-like shaped spring (1) of flat material having two end loops (2, 3) of equal height and one middle loop (4) of about twice this height, all these loops lying within the same plane. The mounted spring is pretensioned in two directions being perpendicular to each other and lying in said plane, the operating force being applied to the top (7) of the middle loop.