To detect the leading edge of a sheet without causing flares on an obtained radiological image, when detecting the leading edge of a stimulable phosphor sheet.

In this scanner, a laser beam 11 is detected by a sensor 30 from the time, prior to the scanning a stimulable phosphor sheet 4 with the laser beam 11 is started, and the leading edge of the sheet 4 is irradiated with the laser beam 11 and the change of the quantity of the laser beam 11 reaching the sensor 30 is detected by a sequence controller 20, whereby the leading edge of the sheet 4 is detected. In such a case, by inclining the flat part 34 of a bracket 32 for attaching the sensor 30 to the reader to a plane perpendicular to the optical axis of a focusing lens 5, the laser beam 11 reflected on the flat part 34 is not made incident on the irradiating position of the laser beam 11 on the sheet 4, and the flares caused by stimulated luminescence emitted from the sheet 4 by the reflected laser beam 11 are prevented.