A power transmission device comprising: a friction clutch transmitting/interrupting power between a drive shaft coupled to a drive source and a first shaft; and a transmission to which power is applied by the first shaft, wherein the transmission has: a second shaft disposed in parallel to the first shaft; a fixed gear disposed to one of the first shaft or the second shaft in a relatively unrotatable manner; an idle gear disposed to the other one of the first shaft or the second shaft in a relatively rotatable manner; at least two annular-shaped hubs coupled to the first shaft or the second shaft and arranged adjacent to the idle gear; and a clutch ring disposed to the outer periphery of each of the hubs so as to be able to move in the axial direction and so as not to be able to rotate with respect to the hub, an end face in the axial direction of the fixed gear or the idle gear is provided with a first dog tooth, an end face in the axial direction of the clutch ring is provided with the second dog tooth which engages with the first dog tooth, at least one of the hub, the clutch ring, the fixed gear, and the idle gear has a thrust generation part which applies thrust in the axial direction to the clutch ring, when the second dog tooth comes into engagement with the first dog tooth, the thrust making another first dog tooth and another second dog tooth separate from each other, and when the maximum torque (Nm) of the drive source is set as x and inertia moment (kgm 2) of the friction clutch is set as y, y ≤ 6 × 10 -6 x is satisfied. a friction clutch transmitting/interrupting power between a drive shaft coupled to a drive source and a first shaft; and a transmission to which power is applied by the first shaft, wherein the transmission has: a second shaft disposed in parallel to the first shaft; a fixed gear disposed to one of the first shaft or the second shaft in a relatively unrotatable manner; an idle gear disposed to the other one of the first shaft or the second shaft in a relatively rotatable manner; at least two annular-shaped hubs coupled to the first shaft or the second shaft and arranged adjacent to the idle gear; and a clutch ring disposed to the outer periphery of each of the hubs so as to be able to move in the axial direction and so as not to be able to rotate with respect to the hub, an end face in the axial direction of the fixed gear or the idle gear is provided with a first dog tooth, an end face in the axial direction of the clutch ring is provided with the second dog tooth which engages with the first dog tooth, at least one of the hub, the clutch ring, the fixed gear, and the idle gear has a thrust generation part which applies thrust in the axial direction to the clutch ring, when the second dog tooth comes into engagement with the first dog tooth, the thrust making another first dog tooth and another second dog tooth separate from each other, and when the maximum torque (Nm) of the drive source is set as x and inertia moment (kgm 2) of the friction clutch is set as y, y ≤ 6 × 10 -6 x is satisfied. a second shaft disposed in parallel to the first shaft; a fixed gear disposed to one of the first shaft or the second shaft in a relatively unrotatable manner; an idle gear disposed to the other one of the first shaft or the second shaft in a relatively rotatable manner; at least two annular-shaped hubs coupled to the first shaft or the second shaft and arranged adjacent to the idle gear; and a clutch ring disposed to the outer periphery of each of the hubs so as to be able to move in the axial direction and so as not to be able to rotate with respect to the hub, an end face in the axial direction of the fixed gear or the idle gear is provided with a first dog tooth, an end face in the axial direction of the clutch ring is provided with the second dog tooth which engages with the first dog tooth, at least one of the hub, the clutch ring, the fixed gear, and the idle gear has a thrust generation part which applies thrust in the axial direction to the clutch ring, when the second dog tooth comes into engagement with the first dog tooth, the thrust making another first dog tooth and another second dog tooth separate from each other, and when the maximum torque (Nm) of the drive source is set as x and inertia moment (kgm 2) of the friction clutch is set as y, y ≤ 6 × 10 -6 x is satisfied.