Moisture amount detection device

A moisture amount detection device, comprising:

• a light source including a semiconductor light emitting element that emits light, the light source projecting the light toward an object, the light flickering at a predetermined frequency;
• a light receiver that receives the light reflected by the object and outputs a detection signal;
• an amplifier that receives the detection signal and outputs an amplified signal obtained by amplifying the detection signal by a predetermined amplification factor;
• a lock-in amplifier that receives the amplified signal and outputs an extracted signal obtained by extracting a signal of the predetermined frequency from the amplified signal;
• an A/D converter that receives the extracted signal, performs A/D conversion on the extracted signal, and outputs a digital signal;
• a low-pass filter whose passband is changeable, and that receives the digital signal and allows a signal of a frequency in the passband in the digital signal to pass through the low-pass filter;
• and
• a controller that controls the passband,
• wherein the controller performs first control to change the passband according to a signal intensity indicated by the digital signal.