A printing apparatus comprising an ink jet head module, the ink jet head module comprising: at least one ink jet head that ejects ink; an ink path that supplies ink to the ink jet head; a joint for connecting the ink path and a fitting portion of a main body of the printing apparatus main body; a handle configured to be operated according to attachment and detachment of the ink jet head module to the main body of the printing apparatus; and the printing apparatus further comprising: the fitting portion of the main body; a fitting mechanism that is configured to insert and extract the fitting portion of the main body of the printing apparatus into and out from the joint in response to movement of the handle; wherein: the fitting mechanism comprises a rack and pinion system; characterized in that the rack and pinion system comprises a circular gear and a handle main body support member of the handle at the side of the joint and in contact with the circular gear; the rack and pinion system further comprising a fitting portion support member of the fitting portion in contact with the circular gear in such a way that the fitting portion moves in the insertion and extraction directions by the fitting mechanism being operated in response to movement of the handle. at least one ink jet head that ejects ink; an ink path that supplies ink to the ink jet head; a joint for connecting the ink path and a fitting portion of a main body of the printing apparatus main body; a handle configured to be operated according to attachment and detachment of the ink jet head module to the main body of the printing apparatus; and the printing apparatus further comprising: the fitting portion of the main body; a fitting mechanism that is configured to insert and extract the fitting portion of the main body of the printing apparatus into and out from the joint in response to movement of the handle; wherein: the fitting mechanism comprises a rack and pinion system; characterized in that the rack and pinion system comprises a circular gear and a handle main body support member of the handle at the side of the joint and in contact with the circular gear; the rack and pinion system further comprising a fitting portion support member of the fitting portion in contact with the circular gear in such a way that the fitting portion moves in the insertion and extraction directions by the fitting mechanism being operated in response to movement of the handle. the fitting portion of the main body; a fitting mechanism that is configured to insert and extract the fitting portion of the main body of the printing apparatus into and out from the joint in response to movement of the handle; the fitting mechanism comprises a rack and pinion system; characterized in that the rack and pinion system comprises a circular gear and a handle main body support member of the handle at the side of the joint and in contact with the circular gear; the rack and pinion system further comprising a fitting portion support member of the fitting portion in contact with the circular gear in such a way that the fitting portion moves in the insertion and extraction directions by the fitting mechanism being operated in response to movement of the handle.