Abstract: A device for inserting information bits into a specific frame structure essentially comprises an elastic memory whose capacity is designed to contain at each time defined by a reduced insertion bit rate D2/N a variable number of bits of words read in a buffer memory written at a reduced bit rate D1/N not yet inserted or not yet reinserted in the outgoing frames, this number varying according to justification commands generated previously, devices for selecting bits contained in said elastic memory for insertion or reinsertion in the outgoing frames, and devices for temporarily blocking the buffer memory read clock if the number of bits to store in the elastic memory exceeds a predetermined limit value.