In principle, except for some special transactions, real estate sales, land leases or building leases in Japan take effect simply by the agreement of the parties concerned without a written contract. No formalities are required.

Of course you need a signed, written agreement in order to confirm the terms and conditions, and to avoid any future disputes. Sometimes notarized agreements are preferable, for example, if you are the lessor and secure the payment of the rent. Normally a deposit is required so that the lessor can secure the funds for overdue rent. Alternatively, if the sales procedures are complicated, or the payment and delivery would not be simultaneously carried out, a notarized agreement could be an option. Anyway you need to discuss with your real estate lawyer whether the use of a notarized agreement would be appropriate for your needs.