A paper sheet discriminating apparatus, comprising: a rotating drum; a plurality of discriminating blades which are arranged in a cylinder within the rotating drum along an inner peripheral surface thereof, to define a discriminating region which is loaded with a plurality of paper sheets (P1, P2, P3) of different thicknesses, transverse end portions of the discriminating blades being superposed with gaps therebetween; a drive device which rotates the rotating drum to revolve the discriminating blades around the center of the discriminating region, thereby causing those paper sheets (P1, P2) which are thinner than the gaps, out of the paper sheets (P1, P2, P3) of the different thicknesses in the discriminating region, to pass through the gaps; and a control device which is adapted to perform control to change a rotating state of the rotating drum driven by the drive device, characterized by further comprising a first measuring device which is adapted to measure the quantity of paper sheets loaded into the discriminating region of the rotating drum and a second measuring device which is adapted to measure the quantity of paper sheets (P1, P2) delivered through the gaps between the discriminating blades, and in that the control device is adapted to perform control to change the rotating state of the rotating drum as a quantity of paper sheets (P1, P2, P3) not less than a predetermined quantity are measured by the first measuring device and is adapted to perform control to stop rotation of the rotating drum as a quantity of paper sheets (P1, P2) not less than a predetermined quantity are measured by the second measuring device. a rotating drum; a plurality of discriminating blades which are arranged in a cylinder within the rotating drum along an inner peripheral surface thereof, to define a discriminating region which is loaded with a plurality of paper sheets (P1, P2, P3) of different thicknesses, transverse end portions of the discriminating blades being superposed with gaps therebetween; a drive device which rotates the rotating drum to revolve the discriminating blades around the center of the discriminating region, thereby causing those paper sheets (P1, P2) which are thinner than the gaps, out of the paper sheets (P1, P2, P3) of the different thicknesses in the discriminating region, to pass through the gaps; and a control device which is adapted to perform control to change a rotating state of the rotating drum driven by the drive device, characterized by further comprising a first measuring device which is adapted to measure the quantity of paper sheets loaded into the discriminating region of the rotating drum and a second measuring device which is adapted to measure the quantity of paper sheets (P1, P2) delivered through the gaps between the discriminating blades, and in that the control device is adapted to perform control to change the rotating state of the rotating drum as a quantity of paper sheets (P1, P2, P3) not less than a predetermined quantity are measured by the first measuring device and is adapted to perform control to stop rotation of the rotating drum as a quantity of paper sheets (P1, P2) not less than a predetermined quantity are measured by the second measuring device.