A gas supplying method of supplying a process gas containing a gas of at least one gaseous species into a process space in a semiconductor manufacturing apparatus includes supplying the process gas by controlling a flow rate value of the gas to be a first value during a first period; supplying the process gas by controlling the flow rate value of the gas to be a second value smaller than the first value during a second period; supplying the process gas by controlling the flow rate value of the gas to be a third value greater than the first value during a third period; and supplying the process gas by controlling the flow rate value of the gas to be a fourth value smaller than the second value during a fourth period, wherein these steps are periodically repeated in a predetermined order.