To provide a device for clamping a cast slab and a method for clamping the cast slab using this device with which in the case of enlarging the width range of the cast slab, the cast slab can surely be clamped and the air cost can be restrained and further, in the case of reconstructing, the constructing period is shortened and the reconstructing cost can be reduced.

The device for clamping the cast slab is provided with a first air circuit for working an air cylinder with the low pressure air, and a second air circuit for working the air cylinder with high pressure air stored in an air tank by increasing the pressure of the low pressure air with an air pressure intensifier. The method for clamping the cast slab using the device is also provided.