An exponential operation device comprises an exponential operation circuit for carrying out the exponential operation of a term x.sup.y formed of data x and data y; and an operation circuit for judging whether the data x supplied by key depression denotes a positive or negative value, and also whether or not the data y supplied similarly by key depression is an integer. Where the operation circuit judges that the data x denotes a negative value and the data y is an integer, then the exponential operation circuit carries out the exponential operation of the term x.sup.y, thereby providing an answer even when the data x denotes a negative value.