A hair holder including a tube configured to allow a hair bundle to be inserted from a one-end opening toward an other-end opening. The hair holder is designed to allow hair treatment to be applied inside the tube to the hair bundle by supplying a hair treating agent into the tube. A hair-treating-agent leak-prevention member is provided on an inner-surface side of the tube in the vicinity of the one-end opening, the hair-treating-agent leak-prevention member achieving an effect of preventing leakage of the agent when pressed against the hair bundle.