PURPOSE: To provide a sheet detection device for a printer device which can set a sheet easily without the sheet being caught by a sheet sensor.

CONSTITUTION: This sheet detection device of a printer device is equipped with a sensor support 22 which supports a sheet sensor 20 of transmission type, provided on the lateral part of a sheet transport path 6 running through a printing part 19, and also a closable element 8 which closes the upper space of the sheet transport path 6. In addition, when setting a sheet 3, the sensor support 22, is retreated from one end to the other end of the sheet transport path 6 together with the sheet sensor 20 using an interlook mechanism 26, if the closable element 8 is opened. Consequently, the sheet 3 can be easily allowed to pass through the printing part and in front of the sheet sensor 20. Further, if the closable element 8 is closed, the sensor support 22 is moved forward to the sheet transport path 6 side together with the sheet sensor 20 using the interlock mechanism 26, so that both light-emitting element 20a and light-receiving element 20b are opposed to both faces of the sheet 3.