In an insulating film formation method, a cycle A in which O3 at a low flow rate is supplied onto a substrate and then O3 supplied is allowed to react with Hf on the substrate in a non-equilibrium state to form a hafnium oxide film is carried out M times (M≧1), and a cycle B in which O3 at a high flow rate is supplied onto the substrate and then O3 supplied is allowed to react with Hf on the substrate in an equilibrium state to form a hafnium oxide film is carried out N times (N≧1). These insulating film formation cycles are defined as one sequence. This sequence is repeated until a desired thickness is obtained, thereby forming a target insulating film.