To calculate time delay compensation wherein, without depending on scanning speed, at advancing and receding, peaks and valleys of both measured value distribution approximately agree with each other.

This scan type sensor is provided with a sensor unit 20 where a sensor measuring weighing, water content ratio, etc., of a to-be-measured sheet 10 is mounted, a sensor driving device 30 which makes the sensor unit 20 reciprocating scan the to-be-measured sheet 10 in its width direction, a measuring position detecting part 40 which generates measuring position pulse signal in the width direction of the sensor unit 20, and the sensor signal processing part 50 which makes the measuring position pulse signal correspond to the measuring signal of the sensor. Then, with the use of sensor delay time X and time interval Tpulse of the measuring position pulse signal, the pulse numbers (to-be-corrected in reciprocation) NpulseW {=Round[2χ/Tpulse]} is obtained, with the use of and advancement correction pulse numbers NpulseF {=Round [NpulseW/2]} and receding correction pulse numbers NpulseB {= Int[NpulseW/2]}, measuring position pulse signal is corrected.