A device for varying a load of a valve system can vary a load acting on a valve spring in accordance with driving conditions of a vehicle. In the device, in a low load mode, only a first valve spring is compressed, and a second valve spring is not compressed. Accordingly, the load acting on the valve spring is reduced, and as such, an enhancement in fuel economy is achieved. In a high load mode, both the first valve spring and the second valve spring are compressed. Accordingly, the load acting on the valve spring is increased, and as such, it is possible to prevent a danger of breakage occurring due to striking components of a valve train system.