1. A wireless communications system comprising: a base station; and a plurality of terminals, respective terminals communicating with the base station by means of interlacing for cyclically using a sub-frame to be subjected to time division multiplex, wherein the base station is configured to notify a respective terminal of load information due to communication between the base station and the terminal, determine at predetermined cycles in the predetermined cycles of a unit of the sub-frame, or shorter than that while the terminal determines load information by the sub-frame based on the load information notified by the base station, thereby selecting an interlace to be used for communication with the base station before communication is executed, wherein the terminal is configured to keep track of the load state at the base station on an interlace-by-interlace basis based on Reverse Activity Bit (RAB) that is generated based on instantaneous values of the measurement results information notified by the base station, and the terminal changes transmission timing according to transition probability information to an interlace that is low in load.