A user interface apparatus made of a grip portion which is gripped by an operator; a contact sensor which is arranged on a surface of the grip portion and which detects a contact position; a sensor information acquiring unit configured to acquire sensor information outputted from the contact sensor; and an input operation acquiring unit configured to acquire a difference between pieces of sensor information respectively acquired at different times and to determine that an input operation corresponding to a predetermined pattern has been performed when the difference conforms to the predetermined pattern.