In Korean traditional architecture, the Gong-po style is divided into the Jusimpo, Dapo and Ikgong. Jusimpo and Chulmok-Ikong, where only Gong-po is placed on the column, differ in form of Gong-po depending on the viewpoint. Since ‘Chulmok-Ikgong’ has been generally regarded as ‘One Chulmok-Two Ikgong’, the precedent researches have been conducted mainly on ‘One Chulmok-Two Ikgong’ in the Gong-po style classification. However, when it comes to ‘One Chulmok’, the style of Ikgong can be organized from the one to three steps and this study is particularly for examining the occurrence and transformation of ‘One Chulmok-One Ikgong’. One of the case study sites, Bonghwa Cheongamjeong was originally built in the 16th century, and is believed to have been repaired from ‘Non Chulmok-One Ikgong’ to ‘One Chulmok-One Ikgong’. Since the beam linked directly to the upper part of a capital, it does not connect the eave trave(architrave) in between. Also, Soro which supports Jangyeo(the architrave strip) has been placed and linked in comparatively lower position. It is confirmed by the signigicant difference in the hierarchy of Gong-po forms in one architecture. The Jeonju-Hyanggyo Daeseongjeon, which was built in the 17th century among the subjects, was similar with ‘One Chulmok-One Ikgong’, but it was found to be the type of Jusimpo form because the bottom of the beam and the top of the Ikong are apart. And Gongan is confirmed at Cheomcha. In the 17th century, it can be seen that Heot-Cheomcha disappeared and Ikgong was started to use as a constant figure. The end of the 18th century, it can be seen that it was changed into a ornament added on Haeng-gong, being seen in the case of Hwaseong Dongjangdae. In conclusion, it can be seen that ‘One Chulmok-One Ikgong’ were developed in both the Jusimpo and Ikong style. The transformation into ‘One Chulmok-One Ikgong’ was inevitable consequence related with an elevation difference between the eave trave and the column trave.