A valve train device for an engine for driving a valve which opens and closes a valve opening of a combustion chamber comprises: a valve drive device comprising a drive member and driving force transmission mechanism. The drive force transmission mechanism is configured to transmit a driving force from the drive member to the valve. The drive force transmission mechanism comprises a transmission portion configured to transmit the driving force from the drive member to the valve and a variable portion configured to continuously change a state of the transmission portion to thereby continuously change an opening duration of the valve or the amount of valve lift. At least part of the variable portion is positioned within in the transmission portion.