PURPOSE: To obtain the LAN system by which a motion picture with less data missing is transferred in two ways by reducing the frequency of collision of lots of data such as picture data in the random access LAN employing the CSMA/CD system.

CONSTITUTION: This system is provided with a system clock 31, computers C1, C2, and the computers C1, C2 are provided respectively with inquiry sections 17, 27 setting a system time and setting it to internal clocks 110, 210, calculation section 18, 28 generating two kinds of time charts by which the computers C1, C2 execute the data transmission timing at an interval alternately based on the time set to the internal clocks 110, 210, returning one time chart to opposite computer and reserving the remaining time chart and control sections 19, 29 controlling the timing of packet transmission according to the time chart of the concerned computer.