A flow control device constructed at a switch device for connecting a plurality of ring networks for exchanging data of a cell among the ring networks. A user device for transmitting a cell carrying data is connected to each ring network, and it can transmit cells within a window counter number. Such flow control device comprises a buffer monitoring unit for monitoring the number of data in an output buffer, a regulation judging unit for comparing the number of data in each buffer with a first threshold value representing state of the buffer which is in danger of overflow, with a second threshold value representing state of the buffer which is not in danger of overflow, and outputting a regulation notice when the data number is grater than the first threshold value while outputting a regulation notice when the data number is smaller than the second threshold value, and a plurality of traffic controlling units for transmitting to the respective ring network a reset cell at a first interval when no regulation notice is received or the release notice is received while transmitting a reset cell at a second interval which is longer than the first interval when the regulation notice is received.