A target gas separation method for separating a target gas from a gas mixture containing the target gas by using three adsorption columns containing an adsorbent for selectively adsorbing the target gas, the method comprising repeating a cycle in each of the adsorption columns, the cycle including: an adsorption step of introducing the gas mixture into the adsorption column to adsorb the target gas in the gas mixture to the adsorbent while discharging non-adsorbed gas from the adsorption column; a rinsing step of introducing rinsing gas into the adsorption column to discharge rinsing off-gas from the adsorption column; and a desorption step of reducing pressure inside the adsorption column to desorb the target gas from the adsorbent and discharging the desorbed gas from the adsorption column, wherein the gas mixture is continuously introduced into any one of the adsorption columns so that the adsorption step is constantly performed in any one of the adsorption columns throughout the cycle, desorption time from beginning to end of the desorption step is made longer than adsorption time from beginning to end of the adsorption step, rinsing time from beginning to end of the rinsing step is made shorter than the adsorption time, and the desorption step in one of the adsorption columns includes a first desorption step for discharging a first desorbed gas from said one of the adsorption columns from beginning of the desorption step after the rinsing step till end of the adsorption step in another of the adsorption columns which is undergoing the adsorption step, and a second desorption step for discharging a second desorbed gas from said one of the adsorption columns after the first desorption step, and the second desorption step in said one of the adsorption columns is performed in parallel with the adsorption step in another of the adsorption columns which is undergoing the adsorption step. an adsorption step of introducing the gas mixture into the adsorption column to adsorb the target gas in the gas mixture to the adsorbent while discharging non-adsorbed gas from the adsorption column; a rinsing step of introducing rinsing gas into the adsorption column to discharge rinsing off-gas from the adsorption column; and a desorption step of reducing pressure inside the adsorption column to desorb the target gas from the adsorbent and discharging the desorbed gas from the adsorption column, wherein the gas mixture is continuously introduced into any one of the adsorption columns so that the adsorption step is constantly performed in any one of the adsorption columns throughout the cycle, desorption time from beginning to end of the desorption step is made longer than adsorption time from beginning to end of the adsorption step, rinsing time from beginning to end of the rinsing step is made shorter than the adsorption time, and the desorption step in one of the adsorption columns includes a first desorption step for discharging a first desorbed gas from said one of the adsorption columns from beginning of the desorption step after the rinsing step till end of the adsorption step in another of the adsorption columns which is undergoing the adsorption step, and a second desorption step for discharging a second desorbed gas from said one of the adsorption columns after the first desorption step, and the second desorption step in said one of the adsorption columns is performed in parallel with the adsorption step in another of the adsorption columns which is undergoing the adsorption step.