An image scanning apparatus comprising: a platen on which an original is placed; a pressure plate openable and closable with respect to the platen; a first angle detector configured to detect that the pressure plate is closed from an open state to a first angle with respect to the platen; a second angle detector configured to detect that the pressure plate is further closed from the first angle to a second angle with respect to the platen; a lamp configured to emit light to the original; a brightness distribution recorder; a processor; and a memory including instructions that, when executed by the processor, causes the processor to perform operations including: upon detection of the first angle by the first angle detector, driving the lamp to emit light to the original and driving the brightness distribution recorder to record a distribution of light reflected by the original of the emitted light as first read data; characterized by upon elapse of a predetermined time from detection of the second angle by the second angle detector, driving the lamp to emit light to the original and driving the brightness distribution recorder to record a distribution of light reflected by the original of the emitted light as second read data; detecting a closed state of the pressure plate based on the second read data; and upon determination of an angle of the pressure plate with respect to the platen being equal to or smaller than a third angle smaller than the second angle in the detection of the closed state, detecting a width of the original in an opening-closing direction of the pressure plate based on a difference between the first read data and the second read data. a platen on which an original is placed; a pressure plate openable and closable with respect to the platen; a first angle detector configured to detect that the pressure plate is closed from an open state to a first angle with respect to the platen; a second angle detector configured to detect that the pressure plate is further closed from the first angle to a second angle with respect to the platen; a lamp configured to emit light to the original; a brightness distribution recorder; a processor; and a memory including instructions that, when executed by the processor, causes the processor to perform operations including: upon detection of the first angle by the first angle detector, driving the lamp to emit light to the original and driving the brightness distribution recorder to record a distribution of light reflected by the original of the emitted light as first read data; characterized by upon elapse of a predetermined time from detection of the second angle by the second angle detector, driving the lamp to emit light to the original and driving the brightness distribution recorder to record a distribution of light reflected by the original of the emitted light as second read data; detecting a closed state of the pressure plate based on the second read data; and upon determination of an angle of the pressure plate with respect to the platen being equal to or smaller than a third angle smaller than the second angle in the detection of the closed state, detecting a width of the original in an opening-closing direction of the pressure plate based on a difference between the first read data and the second read data. upon elapse of a predetermined time from detection of the second angle by the second angle detector, driving the lamp to emit light to the original and driving the brightness distribution recorder to record a distribution of light reflected by the original of the emitted light as second read data; detecting a closed state of the pressure plate based on the second read data; and upon determination of an angle of the pressure plate with respect to the platen being equal to or smaller than a third angle smaller than the second angle in the detection of the closed state, detecting a width of the original in an opening-closing direction of the pressure plate based on a difference between the first read data and the second read data.