To correct the difference of a data input cycle from an external device and the data output cycle of a main device by a device scale as small as possible in an equipment to be mounted to an air frame.

The write and read of the digital data of two memory circuits 18 and 19 are monitored, dummy data are inserted by an identification code generation circuit 51 and a dummy data generation circuit 50 from the head of the next frame for which the read of the data is completed and the formation of stipulated frame format data is continued. At the time, by simultaneously switching a read memory when a write memory is switched and reading the digital data again from the head of the next frame, the difference of cycles in the two memory circuits 18 and 19 is corrected.