ひとりでに

ひ

と

り

で

に

Common wordJLPTN2Freq.FrequencyTop 100,000

Meanings

usually written using kana alone

Describes something happening on its own, without external cause or human intervention; often used for spontaneous events or mechanical actions.

〈物もの〉がひとりでに〈動どう詞し〉for a thing to (do something) on its own, with no one touching it
夜よ中なかに急きゅうにドアがひとりでに開ひらいた。
In the middle of the night, the door suddenly opened by itself.
〈事こと〉がひとりでに治なおるfor something (like an injury or problem) to heal or resolve on its own
小ちいさな傷きずはひとりでに治なおることが多おおい。
Small cuts often heal on their own.

自し然ぜんN4
自然 is the broader, more common word for 'naturally' or 'spontaneously', while ひとりでに specifically stresses that no person or external force caused the event.
自じ動どう的てきN3
自動的 is a formal, technical term for mechanical or systematic automation, whereas ひとりでに is more colloquial and can suggest something happening mysteriously on its own.
自おのずとN1
自ずと and 独りでに both mean something happens by itself without outside help, but 独りでに is more colloquial and often used for machines or physical objects moving on their own.

ひとりでにUsage97%
Usually written in kana; the kanji spellings are less common and may be confusing.
独ひとりでにUsage3%
Kanji spelling using 独り (alone); it is the primary kanji form, but kana is more common.
一人ひとりでに
irregular kanji usage
Irregular kanji usage; 一人 is normally read ひとり but this spelling is not standard for this adverb.

Formed from 独りで “by oneself” followed by the particle に. The combination became a fixed adverb meaning “of itself” or “automatically.”