Provided are a hair bleach composition, hair dye composition and a hair treatment additive having excellent bleaching power, capable of dyeing the hair with a bright and good color, and less damaging to the hair and less irritating to the scalp. Described specifically, they are a two-part hair bleach composition, which contains (a) a nitrogenous compound represented by the following formula (1) or (2): or salt thereof, or (A) a nitrogenous compound having a solubility parameter logP in octanol/water ranging from -1 to 4 and a hydrogen peroxide remaining ratio of from 5 to 90%, or salt thereof, (b) an oxidizing agent, and optionally (c) an alkali agent and, after mixing, has a pH of from 7.5 to 12; a two-part hair dye composition comprising (a) or (A), (b) and (c) and further (d) an oxidation dye or direct dye; and an additive used therefor.