An operation device according to an embodiment includes an operation instruction circuit, an operation circuit, a buffer and a storage area instruction circuit. The operation instruction circuit issues an operation instruction for an operation type of either one of a first operation and a second operation. The operation circuit performs an operation in accordance with the operation instruction, and outputs an intermediate operation result. The buffer stores the intermediate operation result. The storage area instruction circuit specifies an area within the buffer in Which the intermediate operation result is stored, according to the operation type.