An automatic transfer switch, comprising: a drive disk; a first transmission rod and a second transmission rod, transmitting the movement of the drive disk to a first movable contact and a second movable contact respectively, so that when said drive disk moves to a first position, a middle position and a second position respectively, the first movable contact and the second movable contact are driven correspondingly so that said automatic transfer switch is in a first power source closing position, a double-opening position and a second power source closing position; an indicator, fitted and connected to said first transmission rod and said second transmission rod, and configured to be able to move linearly on a first direction, wherein when said automatic transfer switch is respectively in the first power source closing position, the double-opening position and the second power source closing position, said indicator is correspondingly driven to a first indication position, a middle indication position and a second indication position, characterised in that said indicator includes a groove; and furthermore in that the automatic transfer switch comprises in addition: a stopper, able to rotate around a fixed axis, the stopper comprising a first stop portion and a second stop portion extending outward from the center of rotation, and further comprising a projection that fits with said groove, so that the linear movement of said indicator drives the rotation of said stopper through the fitting of said groove and said projection, so that when said indicator is in the first indication position, the middle indication position and the second indication position respectively, said stopper is correspondingly in a first stop position, a middle stop position and a second stop position; and a manual operation disk, coaxial with and rotating synchronously with said drive disk, the manual operation disk comprises a disk body and a first projection portion and a second projection portion projecting radially outward from the disk body, wherein the shapes and positions of said first projection portion and second projection portion as well as said first stop portion and second stop portion are designed such that, in case of contact fusion welding when said automatic transfer switch is in the first power source closing position, in the way of the manual operation disk rotating towards the double-opening position, said first projection portion abuts against said first stop portion so that the manual operation disk cannot move further; in case of contact fusion welding when said automatic transfer switch is in the second power source closing position, in the way of the manual operation disk rotating towards the double-opening position, said second projection portion abuts against said second stop portion so that the manual operation disk cannot move further. a drive disk; a first transmission rod and a second transmission rod, transmitting the movement of the drive disk to a first movable contact and a second movable contact respectively, so that when said drive disk moves to a first position, a middle position and a second position respectively, the first movable contact and the second movable contact are driven correspondingly so that said automatic transfer switch is in a first power source closing position, a double-opening position and a second power source closing position; an indicator, fitted and connected to said first transmission rod and said second transmission rod, and configured to be able to move linearly on a first direction, wherein when said automatic transfer switch is respectively in the first power source closing position, the double-opening position and the second power source closing position, said indicator is correspondingly driven to a first indication position, a middle indication position and a second indication position, characterised in that said indicator includes a groove; a stopper, able to rotate around a fixed axis, the stopper comprising a first stop portion and a second stop portion extending outward from the center of rotation, and further comprising a projection that fits with said groove, so that the linear movement of said indicator drives the rotation of said stopper through the fitting of said groove and said projection, so that when said indicator is in the first indication position, the middle indication position and the second indication position respectively, said stopper is correspondingly in a first stop position, a middle stop position and a second stop position; and a manual operation disk, coaxial with and rotating synchronously with said drive disk, the manual operation disk comprises a disk body and a first projection portion and a second projection portion projecting radially outward from the disk body, wherein the shapes and positions of said first projection portion and second projection portion as well as said first stop portion and second stop portion are designed such that, in case of contact fusion welding when said automatic transfer switch is in the first power source closing position, in the way of the manual operation disk rotating towards the double-opening position, said first projection portion abuts against said first stop portion so that the manual operation disk cannot move further; in case of contact fusion welding when said automatic transfer switch is in the second power source closing position, in the way of the manual operation disk rotating towards the double-opening position, said second projection portion abuts against said second stop portion so that the manual operation disk cannot move further.