A functional unit positioning device for positioning a functional unit detachably attachable to an apparatus body, includes a biasing device that biases the functional unit in a unit-out direction; and a stopper mechanism having a first stopper and a second stopper, the stopper mechanism exerting and releasing control over release of the functional unit. The biasing device biases the functional unit by the biasing device so that the second stopper comes in contact with the first stopper to set the functional unit in a locked position in a unit in-out direction. The biasing device is also configured to change the magnitude of a bias force on the functional unit from low to high when the functional unit is inserted and advanced up to a predetermined position into the apparatus body.