Provided are control device and method for a belt type continuously variable transmission which can improve control stability of secondary hydraulic pressure with the estimated accuracy of a belt slip condition during belt slip control ensured. The device has a primary pulley (42), a secondary pulley (43), and a belt (44), and a secondary hydraulic pressure controller (92) to determine command secondary hydraulic pressure by feedback control based on the deviation (θ) between target secondary hydraulic pressure and actual hydraulic pressure, and control the secondary hydraulic pressure to the secondary pulley (43). A belt type continuously variable transmission mechanism (4) includes a belt slip control means (FIG. 8) to estimate a belt slip condition by monitoring the phase difference (θ) between an oscillation component included in the actual secondary hydraulic pressure and an oscillation component included in the actual transmission gear ratio and control the actual secondary hydraulic pressure to decrease based on the estimation so that a predetermined belt slip condition is maintained. The secondary hydraulic pressure control unit (92) aborts feedback control of the secondary hydraulic pressure during belt slip control and controls the secondary hydraulic pressure by open control.