A valve spring device is provided with a first coil spring and a second coil spring combined in series with each other. The inside diameter (coil inside diameter) of the second coil spring is greater than the outside diameter (coil outside diameter) of the first coil spring. A part of the first coil spring including an end portion along an axis is inserted into the second coil spring, thereby forming a combined spring. The end portion of the first coil spring and an end portion of the second coil spring are connected to each other by a connecting member. The first and second coil springs are compressed along the axis as they are located in series between a cylinder head and a retainer. A shaft of a valve is passed within the coil springs.