A sheet depositing device for a sheet processing apparatus, includes a feeding section for sequentially feeding sheets or sets of sheets from the sheet processing apparatus, at least one sheet stacking element movable along a guide, for facilitating depositing the sheets or sets of sheets fed by the feeding section, and a sensor arrangement for detecting the position of a sheet stacking element along the guide. The sensor arrangement includes a stationary linear array of active elements and a passive element moving in unison with the sheet stacking element. The active and passive elements are of a kind that interact through the use of electric or magnetic fields. Examples of such sensors are an array of conductive fields arranged in parallel to a conductive strip or a second array of conductive fields, and a conductive plate connected to a capacitance meter; and an array of Hall-effect sensors and a magnet.