An image forming apparatus, comprising: an engine unit including an image forming part, a sub-scanning conveyance part and a frame, the image forming part including a carriage having a recording head, and a main scanning moving mechanism configured to move the carriage in a main scanning direction, the sub-scanning conveyance part including a conveyance belt and a driving mechanism configured to drive the conveyance belt in a sheet conveyance direction, the frame configured to support the engine unit; an apparatus main body including a housing; a vibration prevention member between the frame of the engine unit and the housing of the apparatus main body; wherein: the engine unit is provided so as to be attachable to or detachable from the apparatus main body via a front side of the apparatus main body, and configured to be inserted into the housing in a depth direction of the apparatus main body, the frame includes supporting pins (102a-102c) at an upstream side and a downstream side in the sheet conveyance direction and at a lower part of the frame so as to provide three-point support to the engine unit in the apparatus main body; the housing includes holding parts (112a-112c), the holding parts (112a-112c) having engaging holes configured to respectively engage the supporting pins (102a-102c) when the engine unit is inserted into the housing; the supporting pins (102a-102c) project in the depth direction of the apparatus main body when the engine unit is attached to the apparatus main body; the vibration prevention member is fixed to the housing and is configured to press the frame of the engine unit from an upstream side to a downstream side in the sheet conveyance direction; and the engine unit is configured to be rotatable with respect to the supporting pin and the whole of the engine unit is configured to be pressed by the vibration prevention member toward the downstream side in the sheet conveyance direction. an engine unit including an image forming part, a sub-scanning conveyance part and a frame, the image forming part including a carriage having a recording head, and a main scanning moving mechanism configured to move the carriage in a main scanning direction, the sub-scanning conveyance part including a conveyance belt and a driving mechanism configured to drive the conveyance belt in a sheet conveyance direction, the frame configured to support the engine unit; an apparatus main body including a housing; a vibration prevention member between the frame of the engine unit and the housing of the apparatus main body; wherein: the engine unit is provided so as to be attachable to or detachable from the apparatus main body via a front side of the apparatus main body, and configured to be inserted into the housing in a depth direction of the apparatus main body, the frame includes supporting pins (102a-102c) at an upstream side and a downstream side in the sheet conveyance direction and at a lower part of the frame so as to provide three-point support to the engine unit in the apparatus main body; the housing includes holding parts (112a-112c), the holding parts (112a-112c) having engaging holes configured to respectively engage the supporting pins (102a-102c) when the engine unit is inserted into the housing; the supporting pins (102a-102c) project in the depth direction of the apparatus main body when the engine unit is attached to the apparatus main body; the vibration prevention member is fixed to the housing and is configured to press the frame of the engine unit from an upstream side to a downstream side in the sheet conveyance direction; and the engine unit is configured to be rotatable with respect to the supporting pin and the whole of the engine unit is configured to be pressed by the vibration prevention member toward the downstream side in the sheet conveyance direction. the engine unit is provided so as to be attachable to or detachable from the apparatus main body via a front side of the apparatus main body, and configured to be inserted into the housing in a depth direction of the apparatus main body, the frame includes supporting pins (102a-102c) at an upstream side and a downstream side in the sheet conveyance direction and at a lower part of the frame so as to provide three-point support to the engine unit in the apparatus main body; the housing includes holding parts (112a-112c), the holding parts (112a-112c) having engaging holes configured to respectively engage the supporting pins (102a-102c) when the engine unit is inserted into the housing; the supporting pins (102a-102c) project in the depth direction of the apparatus main body when the engine unit is attached to the apparatus main body; the vibration prevention member is fixed to the housing and is configured to press the frame of the engine unit from an upstream side to a downstream side in the sheet conveyance direction; and the engine unit is configured to be rotatable with respect to the supporting pin and the whole of the engine unit is configured to be pressed by the vibration prevention member toward the downstream side in the sheet conveyance direction.