Simple; artless; naive—describing something natural and unadorned, such as a sincere personality, plain style, or rustic charm.
彼女の笑顔はとても素朴で、見ていてホッとする。
Her smile is very simple and sincere, and it puts me at ease.
素朴な村の風景が写真集に収められている。
The photo book contains images of the simple, rustic village scenery.
彼は素朴な疑問を真剣に尋ねた。
He asked a naive/simple question earnestly.