The invention relates to an instrument for treating biological tissue, comprising a housing (4), in which is disposed a ballistic device for generating extracorporeal shock wave-like pressure waves and a transfer element (2) permanently placed on the biological tissue, said element coupling the pressure waves into the body of living creatures, wherein the transfer element (2) couples non-focused, ballistically generated, shock wave-like pressure waves into the biological tissue, said waves generated by an impaction part (10) that is accelerated to a high final velocity of over 5 m/s by a pneumatic medium which is under an operating pressure in a pressure channel (6), said impaction part moving back and forth and impinging on the transfer element (2), wherein the front part of the pressure channel (6) is connected to a back-pressure chamber (8) into which the pneumatic medium, which is located distally in front of the impaction part (10), can flow in toward the transfer element (2) upon acceleration of the impaction part (10). A fast-acting valve (16) releases the pneumatic medium, which is under operating pressure, into the pressure channel (6), wherein a control circuit (17) controls the duration of opening of the valve (16) as a function of at least one or a combination of the following parameters: working pressure, impact frequency or pressure in the back-pressure chamber (8).