A percussion device that breaks an object, the percussion device comprising: a piston; a cylinder for housing the piston, the piston being adapted for reciprocating in the cylinder; a backward port for connecting a front chamber being located at a front side of the cylinder to a hydraulic source; a forward port being formed in a rear chamber being located at a rear side of the cylinder; a forward-backward valve for controlling forward motion and backward motion of the piston by being positioned at one of a forward position for connecting the forward port to the hydraulic source and inducing the piston to move forward and a backward position for connecting the forward port to a hydraulic discharge line and inducing the piston to move backward; a control line (1462a, 1464a) for moving the forward-backward valve to the forward position when being connected to the hydraulic source; a long-stroke port for connecting the hydraulic source to the control line (1462a, 1464a) through the front chamber when the piston is moved backward to a first position, the long-stroke port being formed between the backward port and the forward fort and being connected to the control line (1462a, 1464a); a short-stroke port being connected to the hydraulic source through the front chamber when the piston is moved to a second position which is closer to the front side of the cylinder than the first position, the short-stroke port being formed between the backward port and the long-stroke port and being connected to the control line (1462a, 1464a); and a transmission valve being positioned between the short-stroke port and the control line (1462a, 1464a) and being positioned at one of a long-stroke position for disconnecting the short-stroke port to the control line (1462a, 1464a) and a short-stroke position for connecting the short-stroke port to the control line (1462a, 1464a); wherein when the transmission valve is positioned at the long-stroke position, the piston receives a forward force from a time point when the piston is retreated back to the first position and operates as a long-stroke, and when the transmission valve is positioned at the short-stroke position, the piston receives a forward force from a time point when the piston is retreated to the second position where the piston is located before being retreated to the first position and operates as a short-stroke being shorter than the long-stroke, characterized in that the percussion device comprises a proximity sensor for detecting a bottom dead point of the piston when the object is broken, and a controller configured to: determine a breaking condition based on the detected bottom dead point and transmit a control signal to the transmission valve based on the determined breaking condition. a piston; a cylinder for housing the piston, the piston being adapted for reciprocating in the cylinder; a backward port for connecting a front chamber being located at a front side of the cylinder to a hydraulic source; a forward port being formed in a rear chamber being located at a rear side of the cylinder; a forward-backward valve for controlling forward motion and backward motion of the piston by being positioned at one of a forward position for connecting the forward port to the hydraulic source and inducing the piston to move forward and a backward position for connecting the forward port to a hydraulic discharge line and inducing the piston to move backward; a control line (1462a, 1464a) for moving the forward-backward valve to the forward position when being connected to the hydraulic source; a long-stroke port for connecting the hydraulic source to the control line (1462a, 1464a) through the front chamber when the piston is moved backward to a first position, the long-stroke port being formed between the backward port and the forward fort and being connected to the control line (1462a, 1464a); a short-stroke port being connected to the hydraulic source through the front chamber when the piston is moved to a second position which is closer to the front side of the cylinder than the first position, the short-stroke port being formed between the backward port and the long-stroke port and being connected to the control line (1462a, 1464a); and a transmission valve being positioned between the short-stroke port and the control line (1462a, 1464a) and being positioned at one of a long-stroke position for disconnecting the short-stroke port to the control line (1462a, 1464a) and a short-stroke position for connecting the short-stroke port to the control line (1462a, 1464a); wherein when the transmission valve is positioned at the long-stroke position, the piston receives a forward force from a time point when the piston is retreated back to the first position and operates as a long-stroke, and when the transmission valve is positioned at the short-stroke position, the piston receives a forward force from a time point when the piston is retreated to the second position where the piston is located before being retreated to the first position and operates as a short-stroke being shorter than the long-stroke, characterized in that the percussion device comprises a proximity sensor for detecting a bottom dead point of the piston when the object is broken, and a controller configured to: determine a breaking condition based on the detected bottom dead point and transmit a control signal to the transmission valve based on the determined breaking condition.