PURPOSE: To obtain the delay time adjustment circuit transmitting correctly a data signal string of other carrier even when an error takes place in any carrier when the data signal string of STM-N frame configuration on which plural pointers and plural sets of real information are multiplied by using the multi-carrier digital radio transmission system.
CONSTITUTION: A fixed delay circuit 14 corresponding to a specific Carrier 1, selection circuits 15, 16 corresponding respectively to other carriers 2, 3 and fixed delay circuits 17, 18 are used to generate reference clocks 221, 222, 223 and reference frame pulses 321, 322, 323. The selection circuit is controlled by a pointer discrimination section 13 based on a pointer detected by a pointer detection circuit 12 and selectively provides any of a reception clock 201 obtained from the specific carrier, an output frame pulse 301, reception clocks 202, 203 obtained from each carrier and output frame pulses 302, 303.