The present invention addresses the problem of providing: a top coating agent which forms a protective film demonstrating a beautiful silvery-white appearance, can be adjusted to suppress increases in the friction coefficient even when heat-treated at a high temperature, stabilizes sliding, is strong, and has excellent water resistance, corrosion resistance, and the like; and a fastening member having the protective film formed using said top coating agent. The present invention provides: a top coating agent that includes a polyoxyalkylene amine-based surfactant, a water-soluble modified organopolysiloxane, aluminum flake, and a diluent containing water; and a silvery-white fastening member having a protective film formed using said top coating agent.