An electronic percussion instrument includes an up/down motion detecting apparatus for a hi-hat for detecting up/down motions of the hi-hat regardless of a type of the hi-hat. An interlocked portion moves in response to up/down motions of the hi-hat mounted on an extension rod that constitutes a hi-hat stand. A seat unit does not move in response to up/down motions of the hi-hat. A sensor is provided on the seat unit. A connecting portion connects the interlocked portion and the sensor together and converts up/down motions of the interlocked portion into motions detectable by the sensor.