TOKYO, June 10 -- Japan is where Starbucks proved, beginning three decades ago, that it could run its own stores on foreign soil better than any franchisee. It is now asking investment banks what that proof would fetch.

The company has held preliminary discussions with banks about strategic options for its Japanese business, including a sale of a stake or an initial public offering, Bloomberg News reported on Wednesday. A stake sale could value the unit at 400 billion to 500 billion yen, roughly $2.5 billion and up, and could draw industry buyers as well as private equity. The deliberations are at an early stage and no decision has been made, which is the standard disclaimer attached to processes that have already produced bankers.

Japa...