The disclosed deposition device for forming a thin film using a starter gas comprising an organic metal compound is provided with: a processing container 22; a mounting platform 28 which has a heater 34 for heating the workpiece W; a gas introduction mechanism 80 which introduces the starter gas toward the area more exterior than the outer peripheral end of the workpiece W on the mounting platform 28; an internal partition wall 90 which is disposed such that the lower end of said processing space contacts the mounting platform 28 to form gas outlets 92 between the lower portion of the space and the edges of the mounting platform 28; and a orifice forming member 96 which extends radially inward toward the mounting platform 28 and forms an orifice 98 communicating with the gas outlet 92.