To provide a gradation extension device where dynamic ranges of a plurality of data with different bit widths can be made identical.

In the case of extending data 1 in m-bit into data 2 in n-bit (n>m), data in lower-order (n-m) bits of the data 2 are made equal to data in higher-order (n-m) bits of the data 1. That is, in the case of extending image data C (hexadecimal) in 4-bit into data in 8-bit, the data CC (hexadecimal) are the data in 8-bit. Thus, the gradation extension device is realized, where the dynamic ranges of a plurality of data in different bit widths are made identical to each other.