An encryption apparatus generates two random three-variable polynomials r(x,y,t) and s(x,y,t) to be constituted of like terms of a variable xiyj (where i and j are degrees that are zero or more) when two multiplication results X(x,y,t)r(x,y,t) and f(t)s(x,y,t) are regarded as polynomials of x and y, and generates an encrypted text F from a plaintext polynomial m(t) by using the two multiplication results X(x,y,t)r(x,y,t) and f(t)s(x,y,t).