The present invention provides a process control method in spin etching capable of realizing uniformity in etching amount in etching treatment for even wafers each having various conditions, and achieving uniformity of thickness values among etched wafers. In the present invention, weight of a wafer before etching is measured in units of 1/1000 g, followed by predetermined etching treatment in a spin etching section. Thereafter, weight of the wafer is again measured in units of 1/1000 g after rinsing and drying treatment of the wafer, and then an actual etching amount is calculated from a difference between weight before and after etching of the wafer, confirming an etching rate each time etching to thereby control an etching time.