To provide a gear ratio control device capable of reducing a time taken until a driving force from a power source is output from a continuously variable transmission after starting the power source on an input side of the continuously variable transmission configured as a four-link mechanism.

The gear ratio control device controls a gear ratio at a four-link mechanism type continuously variable transmission. In the gear ratio control device, when the power source is started in a state where the power source is stopped and a vehicle is travelling, an amount of eccentricity is adjusted so that the gear ratio at the continuously variable transmission is at a target value, in parallel with performing start control of the power source.