An image reading device, comprising:
- a platen glass on which an original document is to be placed;
- a platen cover capable of opening/closing the platen glass;
- a light source including a plurality of light emitting elements arranged in a main scanning direction, each of the light emitting elements being configured to irradiate light;
- a light receiving section configured to receive light from the light source;
- a first opening/closing detection section configured to determine on the basis of a first reference whether the platen cover is in an open state or a closed state relative to the platen glass;
- a second opening/closing detection section configured to determine on the basis of a second reference, which is different from the first reference, whether the platen cover is in an open state or a closed state relative to the platen glass;
- and
- an document size determination section configured to determine a size of the original document on the basis of a measurement result from the light receiving section,
- wherein where determination results from the first opening/closing detection section and the second opening/closing detection section indicate the open state when the original document is placed on the platen glass:
- when the determination result from the second opening/closing detection section is changed from the open state to the closed state, the light receiving section obtains first full lighting-up determination data, which is measured with all of the plurality of light emitting elements lighted up;
- when the determination result from the first opening/closing detection section is changed from the open state to the closed state, the light receiving section obtains second full lighting-up determination data, which is measured with all of the plurality of light emitting elements lighted up;
- and
- the document size determination section determines a size of the original document in the main scanning direction on the basis of the first full lighting-up determination data and the second full lighting-up determination data, and
- where the determination result from the first opening/closing detection section indicates the open state, and the determination result from the second opening/closing detection section indicates no open state when the original document is placed on the platen glass:
- when the determination result from the first opening/closing detection section is changed from the open state to the closed state, the light receiving section obtains the second full lighting-up determination data, which is measured with all of the plurality of light emitting elements lighted up, and obtains partial lighting-up determination data, which is measured with some of the light emitting elements of the plurality of light emitting elements lighted up;
- and
- the document size determination section determines the size of the original document in the main scanning direction on the basis of the second full lighting-up determination data and the partial lighting-up determination data.