Provided is a thin film forming apparatus for reducing operation time and cost by forming a film only on a specific portion on substrates. A substrate holding mechanism provided in the apparatus includes: substrate holding members holding substrates in a manner that a part of a non-film forming portion of a substrate overlaps the other substrate and a film forming portion is exposed, a support member supporting the substrate holding members, and a rotation member which rotates the support member. The substrate holding members include: holding surfaces holding the substrates and disposed between a film forming source and the substrates, step portions formed between the holding surfaces in a manner that ends of the substrates respectively contact with the step portions, and opening portions formed on the holding surfaces of the portion corresponding to the film forming portion when the ends of the substrates contact with the step portions.