A power transmission device configured to transmit, from an internal combustion engine to a rotation shaft of a power generator, power input via an output shaft of the internal combustion engine, and to transmit, from a motor to a drive shaft, power input via a rotation shaft of the motor, the power transmission device comprising: a first input shaft disposed in parallel to the drive shaft and configured to be connected to the output shaft of the internal combustion engine; a coupling shaft disposed in parallel to the first input shaft and configured to be connected to the rotation shaft of the power generator; a second input shaft disposed in parallel to the drive shaft and configured to be connected to the rotation shaft of the motor; a first gear mechanism connecting the first input shaft and the coupling shaft; and a second gear mechanism configured to connect the second input shaft and the drive shaft; and a case member, characterized in that: the case member is configured to store lubricating oil; the second gear mechanism includes a driving gear configured to be at least partially kept immersed in the lubricating oil stored in the case member; the case member includes a holding portion (72b, 92) configured to hold lubricating oil that has been scooped up by the driving gear; the first gear mechanism includes a scooping up gear configured to scoop up lubricating oil held in the holding portion; and the case member is configured to guide to the holding portion at least some of the lubricating oil that has been scooped by the scooping up gear. a first input shaft disposed in parallel to the drive shaft and configured to be connected to the output shaft of the internal combustion engine; a coupling shaft disposed in parallel to the first input shaft and configured to be connected to the rotation shaft of the power generator; a second input shaft disposed in parallel to the drive shaft and configured to be connected to the rotation shaft of the motor; a first gear mechanism connecting the first input shaft and the coupling shaft; and a second gear mechanism configured to connect the second input shaft and the drive shaft; and a case member, characterized in that: the case member is configured to store lubricating oil; the second gear mechanism includes a driving gear configured to be at least partially kept immersed in the lubricating oil stored in the case member; the case member includes a holding portion (72b, 92) configured to hold lubricating oil that has been scooped up by the driving gear; the first gear mechanism includes a scooping up gear configured to scoop up lubricating oil held in the holding portion; and the case member is configured to guide to the holding portion at least some of the lubricating oil that has been scooped by the scooping up gear. the case member is configured to store lubricating oil; the second gear mechanism includes a driving gear configured to be at least partially kept immersed in the lubricating oil stored in the case member; the case member includes a holding portion (72b, 92) configured to hold lubricating oil that has been scooped up by the driving gear; the first gear mechanism includes a scooping up gear configured to scoop up lubricating oil held in the holding portion; and the case member is configured to guide to the holding portion at least some of the lubricating oil that has been scooped by the scooping up gear.