A belt-driven continuously variable transmission in which a collision noise of a broken chain belt can be suppressed is provided. In the transmission, a chain belt is applied to belt grooves of pulleys to transmit power therebetween, and a speed ratio is varied by changing a width of the belt groove of at least one of pulleys. The transmission comprises: a guiderail that is contacted to the chain belt to suppress vibrations in the chain belt and that is allowed to rotate with a change in an inclination of the chain belt; and a pushing mechanism that applies a load to the guiderail to rotate the guiderail to alter an inclination of the chain belt in a direction to increase the speed ratio when the chain belt is broken.