A control device for a continuously variable transmission includes a belt type continuously variable transmission and a controller. The controller is configured to calculate an actual gear shift ratio based on rotation speed sensor values from a primary rotation speed sensor and a secondary rotation speed sensor, and to perform gear shift ratio control using feedback control to converge the actual gear shift ratio to a target gear shift ratio. The controller is further configured to stop calculation of the actual gear shift ratio when one of the rotation speed sensor values is less than a first threshold value determined based on a lower limit value of sensor detection accuracy, and stop calculation of the actual gear shift ratio even when one of the rotation speed sensor values is the first threshold value or greater, when a deceleration level of the drive wheel is a prescribed deceleration level or greater.