godan verb (-ru), intransitive verb
be conceited; get a big head; think too highly of oneself
Describes someone becoming arrogant or full of themselves, often due to success or praise. Intransitive; the subject is the person who becomes conceited.
彼は少し成功しただけで思い上がっている。
He's gotten a big head just from a little success.
思い上がる
Don't get conceited.