A signature input device according to an embodiment includes a sign pad configured to output an electronic signature, an input pen configured to input the electronic signature to the sign pad, a three-dimensional position acquisition sensor configured to acquire three-dimensional position information of the input pen, and a control section configured to determine, if the input pen is separated from the sign pad, whether an electronic signature input support instructing motion is included in the three-dimensional position information and, if the electronic signature input support instructing motion is included, perform electronic signature input support processing on the electronic signature.