ナイーブ

na-adjective, noun

naive; innocent; unpretentious

Describes a person or attitude that is innocent, straightforward, and sometimes overly trusting or lacking worldly experience. Can carry a slightly positive or negative nuance depending on context.

from English naive

• 彼かの女じょはとてもナイーブで、人ひとの言いうことをすぐ信しんじてしまう。

  She is very naive and quickly believes what people say.