Sheet detection device and printer

A sheet detection device comprising:

• a sheet guide between a sheet feeding opening into which a sheet is to be inserted and a printing mechanism for printing on the sheet, the sheet guide including a guide surface through which the sheet is to pass;
• a sheet detector including an optical sensor configured to detect a predetermined position of the sheet;
• an opening defined in the guide surface, the sheet detector being inside the opening and the optical sensor being exposed through the opening;
• and
• a transparent guide cover positioned in the guide surface to cover at least a first border position between the sheet detector and the opening on an upstream side in a sheet transport direction,
• wherein:
• the opening extends in a direction orthogonal to the sheet transport direction,
• the sheet detector is configured to be movable along an extending direction of the opening,
• the guide surface is configured with a scale display on an upstream side of the first border position in the sheet transport direction, the scale display being configured to indicate a position of the optical sensor in a movement direction, and
• the scale display is covered by the transparent guide cover.