An apparatus for filling and sealing a bag with a filling opening, comprising: a sealing bar and a pressure bar which are arranged for receiving there between at least a peripheral edge of the filling opening of the bag and for welding of the peripheral edge; a drive which is arranged for moving the sealing bar in relation to the pressure bar between a clamping position and a rest position in which the pressure bar is at a distance from the sealing bar; first retaining means (11, 21) and second retaining means (12, 22) for holding the bag on both sides of the filling opening; characterized in that the apparatus further comprises: a mechanical coupling between the first and / or second retaining means (11, 21; 12, 22) and the sealing bar and between the first and / or second retaining means (11, 21; 12, 22) and the pressure bar, which mechanical coupling is adapted for coupling of a movement of the clamping position to the rest position to a movement of the first retaining means with respect to the second retaining means of a tensioning position to a filling position, in which filling position the distance between the first and second retaining means is smaller than the distance there between in the tensioning position; wherein the first retaining means comprises a first and second clamping block (11, 21), and wherein the second retaining means comprises a first and second clamping block (12, 22); wherein a first side of the bag can be clamped between the first and second clamping block of the first retaining means, and a second side of the bag can be clamped between the first and second clamping block of the second retaining means; the or each first clamping block (11, 12) is mechanically coupled to the or each corresponding second clamping block (21, 22) in the clamping position, such that the first and the second clamping block are forced to move together and a synchronous movement of the pressure bar and of the sealing bar is guaranteed. a sealing bar and a pressure bar which are arranged for receiving there between at least a peripheral edge of the filling opening of the bag and for welding of the peripheral edge; a drive which is arranged for moving the sealing bar in relation to the pressure bar between a clamping position and a rest position in which the pressure bar is at a distance from the sealing bar; first retaining means (11, 21) and second retaining means (12, 22) for holding the bag on both sides of the filling opening; characterized in that the apparatus further comprises: a mechanical coupling between the first and / or second retaining means (11, 21; 12, 22) and the sealing bar and between the first and / or second retaining means (11, 21; 12, 22) and the pressure bar, which mechanical coupling is adapted for coupling of a movement of the clamping position to the rest position to a movement of the first retaining means with respect to the second retaining means of a tensioning position to a filling position, in which filling position the distance between the first and second retaining means is smaller than the distance there between in the tensioning position; wherein the first retaining means comprises a first and second clamping block (11, 21), and wherein the second retaining means comprises a first and second clamping block (12, 22); wherein a first side of the bag can be clamped between the first and second clamping block of the first retaining means, and a second side of the bag can be clamped between the first and second clamping block of the second retaining means; the or each first clamping block (11, 12) is mechanically coupled to the or each corresponding second clamping block (21, 22) in the clamping position, such that the first and the second clamping block are forced to move together and a synchronous movement of the pressure bar and of the sealing bar is guaranteed. a mechanical coupling between the first and / or second retaining means (11, 21; 12, 22) and the sealing bar and between the first and / or second retaining means (11, 21; 12, 22) and the pressure bar, which mechanical coupling is adapted for coupling of a movement of the clamping position to the rest position to a movement of the first retaining means with respect to the second retaining means of a tensioning position to a filling position, in which filling position the distance between the first and second retaining means is smaller than the distance there between in the tensioning position; wherein the first retaining means comprises a first and second clamping block (11, 21), and wherein the second retaining means comprises a first and second clamping block (12, 22); wherein a first side of the bag can be clamped between the first and second clamping block of the first retaining means, and a second side of the bag can be clamped between the first and second clamping block of the second retaining means; the or each first clamping block (11, 12) is mechanically coupled to the or each corresponding second clamping block (21, 22) in the clamping position, such that the first and the second clamping block are forced to move together and a synchronous movement of the pressure bar and of the sealing bar is guaranteed.