The parties are free to make their contract with whom they want. But by the law of representation, in the cases, when an agent acts in the name of a principal, its acts bind the principal and the other party directly each other. The agent is not bind personally to the other party. But, the actor acts on instructions and on behalf of, but not in the name of, a principal, the other party neither knows nor could have known that the intermediary acts an agent, the intermediary and the other party may be bound to each other. Sometimes, an actor, in spite that he is the true beneficiary of the contract, may conclude a contract under the name of a principal, who has no intention of bounding any legal obligations. When the position of a lessor is becoming to success from an assignor (also lessor) to an assignee at the housing lease protection law, also the returning debt on assurance deposit justly becomes succession, in this case, it must interpret that a lessor have to stand on the position of guarantor, in case of returning assignee`s the debt on assurance deposit. This regulation is become to help a lessee who isn`t protected at the housing lease protection law in case of problem about the returning debt on assurance deposit also. Namely, this regulation will become to help in true feelings to the weak in our society, which stand on the position of a lessee with reason which assurance deposit is only cheap, though he will know or not know about that it cannot be guaranteed returning on assurance deposit from exchange value of the residence. The contents of contract are to be interpreted according to the common intention of the parties in spite of the literal meaning of the words. If an intention cannot be known, it is necessary to be interpreted according to the understanding that a reasonable person of the same kind as the other party would have had in the same circumstances. In determining the intention of a party or the understanding a resonable person would have had, due consideration to be given to all circumstances of the case including the characteristic of the contracts, the contents, the negotiations, an practices which the parties have established between themselves, and usages.