To provide the means for preventing a slip spring from jumping out from a spring housing with less cost as much as possible while a flat structure is maintained as much as possible by improving the system of the spring housing having a base, a driving gear and a concentric sliding face arranged at the outer end part of the slip spring, which is for the slip spring used for compensating gear idleness in the driving mechanism of a tachograph.

A flange 5 is integrally formed on the base 2. The sliding face 6 is formed on the inner side of the flange. A cover disk fixing the slip spring in an axial direction in the spring housing 4 is provided. Restraining hooks 7, 8 and 9 facing the direction of the flange 5 are formed at the base 2 and they can be fixed to the end face side of the flange 5.