Function of user operable sections determined by relative positions of sliding units

A portable apparatus, such as a portable telephone, having two units 100, 200 that slide relative to each other such that the function of a user operation section depends upon the relative positions of the two units 100, 200. The front-side unit 100 has a display 101 and a secondary operation section 102, and the back-side unit 200 has a main operation section 201. A position detector detects the relative positions of the units 100, 200 and a control unit changes the user input function performed by either or both of the operation sections 102, 201. Additionally, an optical function section may be provided on the back of the front-side unit 100 including a CCD camera (104 fig.3A) and a fingerprint input section (105 fig.3A).