Spraying machine comprising: - a support frame adapted to be connected to a towing vehicle, - an oscillating counter-frame connected to the support frame by means of an oscillating arrangement, - a spray boom comprising at least: ∘ a first arm hinged to the counter-frame according to a hinging axis, and ∘ a plurality of spraying nozzles installed on the first arm for dispensing a liquid product, the first arm being movable about said hinging axis between an open position and a closed position, - a locking arrangement adapted to prevent the counter-frame from oscillating with respect to the support frame, in at least a first oscillation direction, when the first arm is in the closed position, characterized in that said locking arrangement comprises: ∘ a plate pivoted on the counter-frame according to a fulcrum axis parallel to the hinging axis of the first arm, ∘ a spring having one end connected to the first arm and an opposed end connected to the plate, ∘ an indentation made in the plate, and ∘ a pin fixed to the support frame and having longitudinal axis parallel to the fulcrum axis of the plate, wherein the plate is adapted to oscillate about the fulcrum axis between an unlocking position, in which the indentation is released from the pin allowing the oscillation of the counter-frame with respect to the support frame, and a locking position, in which the indentation is coupled to the pin preventing the oscillation of the counter-frame with respect to the support frame in at least said first oscillation direction, and wherein the spring is configured to rotate the plate about the fulcrum axis towards the unlocking position, when the first arm is in the open position, and to rotate the plate about the fulcrum axis towards the locking position, when the first arm is in the closed position. - a support frame adapted to be connected to a towing vehicle, - an oscillating counter-frame connected to the support frame by means of an oscillating arrangement, - a spray boom comprising at least: ∘ a first arm hinged to the counter-frame according to a hinging axis, and ∘ a plurality of spraying nozzles installed on the first arm for dispensing a liquid product, the first arm being movable about said hinging axis between an open position and a closed position, ∘ a first arm hinged to the counter-frame according to a hinging axis, and ∘ a plurality of spraying nozzles installed on the first arm for dispensing a liquid product, - a locking arrangement adapted to prevent the counter-frame from oscillating with respect to the support frame, in at least a first oscillation direction, when the first arm is in the closed position, characterized in that ∘ a plate pivoted on the counter-frame according to a fulcrum axis parallel to the hinging axis of the first arm, ∘ a spring having one end connected to the first arm and an opposed end connected to the plate, ∘ an indentation made in the plate, and ∘ a pin fixed to the support frame and having longitudinal axis parallel to the fulcrum axis of the plate, wherein the plate is adapted to oscillate about the fulcrum axis between an unlocking position, in which the indentation is released from the pin allowing the oscillation of the counter-frame with respect to the support frame, and a locking position, in which the indentation is coupled to the pin preventing the oscillation of the counter-frame with respect to the support frame in at least said first oscillation direction, and wherein the spring is configured to rotate the plate about the fulcrum axis towards the unlocking position, when the first arm is in the open position, and to rotate the plate about the fulcrum axis towards the locking position, when the first arm is in the closed position.