In a transmission timing control apparatus, a state variable signal affected by a phase representing the data transmission timing of a neighboring node is used to determine the data transmission timing of the own node. A node information transmitter/receiver transmits source identification information particular to the own node and source node information of a data signal received by the own node, and receives node information transmitted from the neighboring node. A neighboring node information collecting circuit collects neighboring node information of all neighboring nodes having received data signals, based upon the source identification information received by the node transmitter/receiver and the source node information. A collision determination circuit compares in number neighboring nodes to which the transmission timing determining circuit is related as to the control of the data transmission timing with nodes based on the all neighboring node information to determine the probability of a collision between data transmissions.