This production method produces an underwear-type clothing article (1) provided with a covering material (11) having a side seal part (S). In this production method, the continuous body of the covering material (11) in which elastic members (14 to 16) are arranged in an extended state is overlapped between band-shaped sheets. Then, the overlapped continuous body of the covering material (11) is subjected to heat sealing by melting the constituent fibers of the band-shaped sheets of the covering material (11) while extending the elastic members (14 to 16) at an interval, and a sealed part (S) is formed on the heat sealed region. Subsequently, the melted constituent fibers are forcibly cooled and a heat sealed region (HT) is cooled while extending the elastic members (14 to 16). Finally, the underwear-type clothing article (1) having the side seal part (S) is formed by cutting off the sealed part (S).
