Patent ID: 8824920

Claim:
A mount-demount mechanism for a unit comprising: a unit that is mountable on and demountable from an apparatus main body; a pair of slide rails that are disposed on the apparatus main body and slidably support both surfaces parallel to a mount-demount direction of the unit; a unit-side roller a pair of which is disposed on both sides parallel to the unit mount-demount direction of the unit and includes a first roller that is disposed downstream in a unit insertion direction and a second roller that is disposed upstream in the unit insertion direction; a positioning portion that is formed on both sides of the unit downstream in the unit insertion direction with respect to the first roller; a guide portion that is formed on the device main body and guides the positioning portion; a rail groove that is formed on the slide rail and includes a lower rail and an upper rail with which the unit-side roller engages; and a cut-away portion that is formed on a portion of the upper rail or the lower rail and places the unit at a predetermined position in the apparatus main body by making either of the first roller and the second roller run off from the rail groove, wherein when the first roller passes the cut-away portion, the positioning portion is supported by the guide portion and the second roller is supported by the rail groove, so that the first roller is prevented from running off from the cut-away portion, and the second roller reaches the cut-away portion and runs off the rail grove, so that the positioning portion is positioned by a positioning hole that is formed on the guide portion.