To provide an insulin resistance-improving agent, and the application thereof. The insulin resistance-improving agent contains an eggshell membrane component, for example, an eggshell membrane-containing powder or a soluble eggshell membrane component. Further, the eggshell membrane-containing powder to be used is a fine powder, and preferably has a volume average particle size of 6 μm or less, and/or a volume maximum particle size of 20 μm or less, but these particle sizes are not limited to the values.