Disclosed is an information detecting device capable of reducing fluctuation in detection accuracy. A recording sheet P transported through a transport path comes into contact with a displacing member, and, in this state, a motor is driven to rotate a cam, and the resilient force of a coil spring causes a pressurizing member to collide with the recording sheet P. The impact force at that time is detected by a detection sensor, and transmitted to a sheet material information obtaining means. Then, on the basis of the detection result, it is possible to detect the type, density, thickness, surface irregularities, etc. of the recording sheet P. At this time, the recording sheet P is in contact with the displacing member, whereby it is possible to reduce fluctuation in detection accuracy due to positional deviation of the recording sheet P.