A near infrared ray activation type positive resist composition comprising (A) a vinyl-based polymer having a monomer unit having an alkali-soluble group blocked by an ether having an alkenyl group next to an ether oxygen, (B) a photothermal converting substance generating heat by a light in the near infrared region, (C) a thermal acid generator generating an acid by heat, can provide a near infrared ray activation type positive resist composition which can be subjected to an exposure treatment in a complete bright room such as under a white light and the like, gives desired sensitivity and resolution, and of which baking treatment conditions can be relaxed or a baking treatment can be omitted, and a pattern formation method using the same.