For example, four driver transistors are arranged in wells so as to adjoin both sides of each of two element isolation regions. Two pairs of cross-coupled sense transistors are arranged in the wells at positions farther from the element isolation regions than the driver transistors are. Such an arrangement provides more than a certain distance between the sense transistors and the respective corresponding element isolation regions. This reduces the effect of a phenomenon that threshold of a transistor varies according to a distance from an element isolation region. As a result, it is possible to exactly match the characteristics of each pair of cross-coupled transistors.