A reciprocating-piston machine, in particular an internal combustion engine with a variable compression ratio, having a length adjustment device arranged in a connecting rod and can be activated by way of a switching unit arranged in the connecting rod, wherein an actuating mechanism is operatively connected to the switching unit in the region of a connecting rod bearing in order to introduce a switching pulse into the connecting rod. The actuating mechanism has a transmission means arranged in the region of the connecting rod bearing, and the switching unit has at least one switching valve which is arranged in the connecting rod body of the connecting rod and the valve body, which can be displaced substantially in the direction of the rotational axis of the connecting rod bearing, and can be deflected out of a dosed position into an open position by way of the transmission means.