A transmission period determination method, etc. capable of setting IPT transmission period by using general-purpose wireless modules and existing drivers is provided. A wireless communication system is a wireless backhaul. A route is established from a core node to a slave node. The core node assigns a specified transmission period and transmits a plurality of training packets to the slave node. The slave node transmits, to a transmission period determination device, the number of training packets received first and last and the number of training packets received without overlap. An estimation unit estimates a training time, the time for the slave node to receive the training packets. A calculation unit calculates a training metric candidate. An updating unit compares the values of the current training metric and the training metric candidate to determine the IPT transmission period.