Guarantor or surety: a person who takes responsibility (financially or legally) if another fails to meet obligations, such as for rent or loans.
アパートの契約には保証人が必要だった。
A guarantor was required for the apartment contract.
彼は友人のために保証人になることを断った。
He refused to act as guarantor for his friend.
保証人がいると契約の審査が通りやすくなる場合がある。
Having a guarantor can sometimes make it easier to pass contract screening.