Image reading apparatus

An image reading apparatus comprising:

• a transport unit comprising transport rollers which are configured to transport a document;
• a reading unit comprising first and second sensors which are configured to read an image of the document which is transported by the transport unit;
• a sonic wave sensor which outputs a sonic wave to a document which is transported by the transport unit, and detects an attenuation rate of the sonic wave;
• and
• a controller which generates image data as data of the image which is read by the reading unit,
• wherein, as operation modes for performing reading in the reading unit, there are a first reading mode and a second reading mode in which resolutions of the generated image data are the same, and transport speeds are different from each other,
• wherein the controller transports the document at a low speed when reading the document in the second reading mode compared to a case in which the document is read in the first reading mode,
• wherein an operation mode of reading a document with a first thickness is set to the first reading mode, and an operation mode of reading a document with a second thickness which is thinner than the document with the first thickness is set to the second reading mode, and
• wherein the controller determines that the document which is transported by the transport unit is thin when an attenuation rate of a sonic wave which is detected by the sonic wave sensor under a circumstance in which the document is transported by the transport unit is less than a determining attenuation rate, and executes the second reading mode.