The present invention relates to a locking arrangement for a terminal device of a telecommunication system. To improve the operating reliability of the terminal device, the attachment and locking of the structural elements changeable by the user to the rest of the device structure is improved by a locking device which consists of a solid piece (100) to be fitted into the terminal device in the different places of the frame part of which one has formed separate spring-like locking elements, each of which functions as a locking device of some structural element of this kind of the terminal device. The first spring-like locking element (20) may e.g. be adapted to lock the accumulator of the terminal device to the accumulator space reserved for it, and the second locking element (40) to lock the smart card of the terminal device to the space reserved for it in the terminal device. In the same locking piece there may also be locking elements (30, 31) for locking the accumulator cover in place.