Emotional advertisement has recently caught attention as an effective tool of marketing communication. However, this research has been scarce in the online context. This research investigates the impact of online emotional advertisement on customer behavior with the moderator of brand attachment. Since brand attachment reflects certain conditions of the emotional state of consumers, it is assumed to be related to the effect of emotional appeal in advertising. We showed three types (emotional, informational, and mixed) of online movie advertisements of two items to Japanese undergraduate students, and conducted two questionnaires: one on the brand attachment and the other on purchase intention and engagement behavior. Results demonstrated that online emotional advertisement impacted both engagement behavior and purchase intention, while online informational one did so only on the purchase intention. The moderating effect of brand attachment was confirmed only in online emotional advertisements of one item on engagement behavior.