An image forming device comprising: a casing formed with a first opening, and an upper cover for opening and closing the first opening; a plurality of photosensitive bodies (61A, 62A, 61A'); a plurality of developing devices (200, 62H, 200') respectively corresponding to the plurality of photosensitive bodies (61A, 62A, 61A'); and a plurality of developer accommodating devices (100, 62G, 100') that accommodates and supplies developer respectively to the plurality of developing devices (200, 62H, 200'), the plurality of developer accommodating devices (100, 62G, 100') including a first developer accommodating device (100, 100') that is individually replaceable and separable from the corresponding developing device (200, 200') and a second developer accommodating device that is replaceable integrally together with the corresponding developing device; wherein another one of the plurality of developer accommodating devices (100, 100') located at a most downstream side in the arrangement direction is the first developer accommodating device (100, 100') accommodating black developer, and each of the developer accommodating devices other than the another one of the plurality of developer accommodating devices (100, 100') is the second developer accommodating device, characterized by a retaining member that retains the plurality of photosensitive bodies (61A, 62A, 61A') arranged in an arrangement direction, the plurality of developing devices (200, 62H, 200'), and the plurality of developer accommodating devices (100, 62G, 100') at fixed positions within the casing, the casing further comprising a second opening and a front cover for opening and closing the second opening, the upper cover being configured to open the first opening when the front cover is closed, the retaining member being capable of being pulled out from the casing in the arrangement direction through the second opening and being movable between a first position where the plurality of photosensitive bodies (61A, 62A, 61A'), the plurality of developing devices (200, 62H), and the plurality of developer accommodating devices (100, 62G, 100') are inside the casing and a second position where one of the plurality of developer accommodating devices located at a most upstream side in the arrangement direction is replaceable, and in that the first developer accommodating device (100, 100') is replaceable from above and configured to be passed through the first opening when the retaining member is at the first position. a casing formed with a first opening, and an upper cover for opening and closing the first opening; a plurality of photosensitive bodies (61A, 62A, 61A'); a plurality of developing devices (200, 62H, 200') respectively corresponding to the plurality of photosensitive bodies (61A, 62A, 61A'); and a plurality of developer accommodating devices (100, 62G, 100') that accommodates and supplies developer respectively to the plurality of developing devices (200, 62H, 200'), the plurality of developer accommodating devices (100, 62G, 100') including a first developer accommodating device (100, 100') that is individually replaceable and separable from the corresponding developing device (200, 200') and a second developer accommodating device that is replaceable integrally together with the corresponding developing device; wherein another one of the plurality of developer accommodating devices (100, 100') located at a most downstream side in the arrangement direction is the first developer accommodating device (100, 100') accommodating black developer, and each of the developer accommodating devices other than the another one of the plurality of developer accommodating devices (100, 100') is the second developer accommodating device, characterized by a retaining member that retains the plurality of photosensitive bodies (61A, 62A, 61A') arranged in an arrangement direction, the plurality of developing devices (200, 62H, 200'), and the plurality of developer accommodating devices (100, 62G, 100') at fixed positions within the casing, the casing further comprising a second opening and a front cover for opening and closing the second opening, the upper cover being configured to open the first opening when the front cover is closed, the retaining member being capable of being pulled out from the casing in the arrangement direction through the second opening and being movable between a first position where the plurality of photosensitive bodies (61A, 62A, 61A'), the plurality of developing devices (200, 62H), and the plurality of developer accommodating devices (100, 62G, 100') are inside the casing and a second position where one of the plurality of developer accommodating devices located at a most upstream side in the arrangement direction is replaceable, and in that the first developer accommodating device (100, 100') is replaceable from above and configured to be passed through the first opening when the retaining member is at the first position.