The effect of Internet advertising is increasing due to the prevalence of smartphones and high-speed communication. Among them, video advertisements featured on video sharing platforms, such as YouTube, are attracting attention. Effective distribution methods on these platforms are being actively discussed. However, research on the insertion timing of video advertisements (beginning, middle, or end) has been insufficient. Since viewers’ attention differs in the beginning, middle, and end of video content, it is presumed that the effect of the advertisements on viewers will change based on their presentation time. In this study, we tested the following two hypotheses for video advertisements of tea and fitness gyms on YouTube: (1) The video advertisements inserted in the middle of the video are more memorable than those inserted in the beginning and end. (2) The video advertisements inserted in the beginning and end of the video have more influence on purchase intent than those inserted in the middle. Randomized controlled trials were conducted and both hypotheses were supported. Therefore, there is a need for video platform operators to build a mechanism to set the insertion timing of video advertisements according to the objective of the advertiser.