A medium transport device includes a restricting unit that is provided in a device main body, and that is coupled with an attaching and detaching operation of a unit body, which configures a portion of a transport pathway, to the device main body. The restricting unit changes between a first state that allows the cover to attain a closed state with respect to the device main body and a second state that restricts the cover from attaining a closed state with respect to the device main body.