Resolving the brake squeal that occurs under various environments is a major topic, and a resolution method is eagerly anticipated. We focused on the phenomenon that, amid various environmental conditions, squeal occurs easily when an automobile has been left standing in a cold environment. We checked the details focusing on the friction coefficient (hereafter, μ). As a result, we found that μ increases when squeal is generated, and that the sliding surface film contributes to the μ behavior. We studied measures to be taken to increase the μ in cold conditions.