The present invention relates to [1] a hair cosmetic containing (A) a specified quaternary ammonium salt, (B) a dimethylpolysiloxane having a weight average molecular weight of 100 or more and 3,000 or less, and water, the hair cosmetic being used by applying on the hair and then rinsing away, wherein the content of the component (B) is 0.3 mass% or more and 60 mass% or less, and a receding contact angle (θR) of water droplet as measured by the expansion-contraction method with respect to the surface of a polyethylene plate which is applied with the hair cosmetic and then subjected to water washing is 82° or more and 110° or less； and [2] a treatment method of hair including (I) a step of applying the hair cosmetic on the hair and spreading it over the entire hair, and (II) a step of rinsing away the hair cosmetic with water from the entire hair. In accordance with the hair cosmetic of the present invention, when used by applying on the shampooed hair and rinsing away, before starting a drying behavior of the hair, the moisture remaining among the hairs is naturally drained by gravity as far as possible, thereby making it possible to shorten the drying time of the hair and to reduce a load of the drying behavior.
