The invention discloses a straight grinding machine. The straight grinding machine comprises a first shell, the left end of the first shell is fixedly connected with a second shell, the right end of the first shell is fixedly connected with a third shell, a motor is installed inside the first shell, and the tail end of an output shaft of the motor is connected with a transmission shaft through a coupler; and the tail end of the transmission shaft penetrates through the right end face of the third shell, the right end of the transmission shaft is fixedly connected with a connecting shaft, and the interior of the third shell is fixedly connected with a first bearing. According to the straight grinding machine, the motion trail of the whole grinding machine in the grinding process can be controlled so that the grinding machine can move linearly for grinding, and therefore linear welding scars can be ground more accurately, the working time can be saved, on the one hand, the working efficiency is effectively improved, on the other hand, the face which does not need to be ground is protected, and the quality of workpiece products is improved; in addition, the switchable abrasive belt grinding mode is added, so that the device is more comprehensive in function, and the overall functionality of the device is enhanced.