MOISTURE AMOUNT DETECTION DEVICE

A moisture amount detection device (1) includes: a light source (10) that projects light that flickers at a predetermined frequency toward an object (2); a light receiver (30) that receives the light reflected by the object (2) and outputs a detection signal; an amplifier (40) that outputs an amplified signal obtained by amplifying the detection signal by a predetermined amplification factor; a lock-in amplifier (50) that outputs an extracted signal obtained by extracting a signal of a predetermined frequency from the amplified signal; an A/D converter (60) that performs A/D conversion on the extracted signal, and outputs a digital signal; a second low-pass filter (72) whose passband is changeable, and that allows a signal of a frequency in the passband in the digital signal to pass therethrough; and a controller (71) that performs first control to change the passband according to a signal intensity indicated by the digital signal.