A coating film forming method includes: rotating a substrate at a first rotation speed in a coating cup with an upper surface open, and supplying and diffusing a coating solution for forming a coating film on the substrate; and after the supplying and diffusing the coating solution, drying the substrate by exhausting air through a gap between an annular member arranged above the substrate with centers thereof being located on a same axis and the front surface of the substrate, while rotating the substrate at a second rotation speed lower than the first rotation speed, wherein at the drying the substrate, a flow velocity of the air exhausted through the gap is higher than a flow velocity of air supplied from above the substrate in the coating cup to the substrate.