To provide a method for treating a milk product enabling long-term preservation of the milk product by freezing, and sufficiently preventing occurrence of disadvantage caused by freezing, to provide the milk product treated by the treating method and to provide a western-style cake containing the milk product.

The method for treating the milk product 5 comprises using a freezing device 10. The freezing device has a magnetic field producing device 2 imparting the milk product 5 with a magnetic field and changing the intensity of the magnetic field with the lapse of time, and a magnetic field control device 3 controlling the production of the magnetic field from the magnetic field producing device 2 and the intensity of the magnetic field. The magnetic field producing device 2 is controlled to impart the milk product 5 thrown into a freezing device body 101 with the magnetic field of a predetermined intensity for a predetermined time T (minute), and stop or decrease the magnetic field from the magnetic field producing device 2. The predetermined time T is determined based on the conditions such as the weight and the thickness of the milk product 5. The predetermined time T is determined preferably through considering the cooling speed of the freezing device 10.