"The Structure of Fiduciary Duties As Approached Through Law & Economics"(in Japanese)

We examine two issues on duciary duty.First,what is the essential structure of duciary duty?Second,does duciary duty have elements of a mandatory rule? Concerning the rst question,the formation of a duciary relationship involves the di culty of writing a contract on the acts that the duciary has to do,and the outcomes of the acts.Especially,duciary duty is used when writing a contract on outcomes is so di cult that an outcome-based contract cannot attract an agent.We interpret duciary duty as an attempt at coping with this di culty by (1) a defensive incentive structure that prohibits the misappropriation of the principal's 'asset' by the agent and (2) the court's ex-post supervision on veri able acts of misappropriation. For duciary duty to have elements of a mandatory rule,(1) the rule itself should be clear and speci c and (2) the extent that the rule applies should be also clear.Furthermore,they must pass the cost-bene t test of Kanda and Fujita:"The value of bene ts,which accrues to the society from setting a rule as a mandatory rule, should exceed the cost of sacri ce,which accrues to the society from compelling the parties to obey the arrangements of the mandatory rule." (Hideki Kanda and Tomotaka Fujita)(1998)