The aging of construction workers and the decrease in the number of young people entering the workforce have raised concerns about the decline in technical skills in the construction sector. This study aims to reveal chronological changes in the skill level of local construction engineers in terms of age, period, and cohort effects by conducting a cohort analysis of time-series changes in their skill level. A questionnaire survey was conducted on engineers belonging to construction companies (engineers of prime contractors) that undertook earthwork projects in Ehime Prefecture, and Age-Period-Cohort (APC) analysis was used to decompose the time-series changes in their skill levels into the three effects of age, period, and cohort. The results showed that the skill level of the generation that entered the workforce 20-25 years ago (1997-2002), when social criticism of the construction industry increased, tended to be the lowest. The skill level of the younger generation who entered the construction industry within 10 years was also generally lower than that of the veteran generation. Finally, based on the above results, we discuss the actual situation of the decline in technical skills in the local construction sector and summarize the issues to be examined in the future.