Sheet characteristic detection device and image forming system

A sheet characteristic detection device comprising:

• a housing provided with an opening;
• a light emitter housed in the housing and emitting light toward the opening;
• a light receiver housed in the housing and receiving reflected light of the light emitted from the light emitter;
• a shutter housed in the housing and switchable between a closed state in which the shutter closes the opening and an open state in which the shutter opens the opening;
• and
• a drive mechanism housed in the housing and driving the shutter,
• the sheet characteristic detection device detecting a characteristic of a sheet by applying light from the light emitter to the sheet through the opening and detecting reflected light that is reflected by the sheet and that transmits through the opening by the light receiver,
• the sheet characteristic detection device including a hardware processor that detects whether the shutter is opened or closed, using a phenomenon in which the shutter blocks light from the light emitter or reflected light of the light during opening or closing of the shutter.