PURPOSE: To obtain a waist regulator capable of readily increasing, reducing or changing the waist size good in appearance by enabling the waist size of a side part of clothes to mutually approach and separate and arranging a pair of guide members and engaging parts in a specific state.

CONSTITUTION: A pair of guide rails 3 and 5 in the form of long plates are respectively connected to a pair of divided belt parts (1a) and (1b) to form engaging parts (3a) and (5a) of nearly C-shaped cross section in opposite side edges of the respective guide rails 3 and 5. A slit 6 is formed in the vertical directions in a lining fabric (4b) of a front pocket connecting both the belt parts (1a) and (1b). On the other hand, nearly cylindrical engaging parts (7b) and (7c) capable of sliding in the respective engaging parts (3a) and (5a) are integrally formed in both the front and the rear side edges of an attaching piece 7 of nearly a truncated shape corresponding to a gap between both the guide rails 3 and 5. Thereby, the attaching piece 7 can be engaged and held at a prescribed height along the guide rails 3 and 5 with a bonding cloth 8 to fix a holding piece 9 provided with a prescribed decoration in nearly the central part of the attaching piece 7.