To provide an inexpensively and simply constructed contact detection system working with high reliability.

A touch sensor 10 has a keyboard having a key defining a contact position 14. The key responds to at least one of a capacitive interaction and an electromagnetic interaction with a user 16 during the contact. The key has a control circuit related to the key. The control circuit outputs a control signal. The dimension of the control signal shows interaction quantity between the user and the key during the contact. A controller is connected to the control circuit to analyze fluctuation in the dimension of the control signal over a predetermined period for identifying the contact.