To provide a device comparing associative memory, a method of controlling the comparing device, and associative memory.

The associative memory cell is a memory cell made of a first transistor T1 for storing data bits and a second transistor T2 for storing the complements of the data bits. Each transistor is formed on a semiconductor-on-insulator substrate; and each transistor has a memory cell including a front control gate and a back control gate BG1, BG2 so as to cut off the transistors, and a comparator circuit applying a nominal read-out voltage to each the front control gate to operate in a read mode; controlling the back control gate BG1, BG2, for one of them by bits (DATA) and the other by the complements (DATAb) of bits; cutting off the pass transistor among them when the bits (DATA) and stored bits agree one another; and checking whether there is a current flowing in the source line SL connected to each source.