The invention provides a dog clutch of a vehicle power transmission device suppressing wear which may occur in a sliding pad of a shift fork at an engagement position of a sleeve. Each of the inner circumferential teeth (56s) and the outer circumferential teeth (54s) has the inclined tooth surfaces (86, 88) the tooth thicknesses of which become larger as the inner circumferential teeth and the outer circumferential teeth approach each other. When a sleeve (56) is moved to the engagement position (P2) by the shift fork (60), the sleeve (56) is held in contact with the side surface (48a) of an idler gear (48). Therefore, when the sleeve (56) is moved to the engagement position (P2), the sleeve (56) is held such that the sleeve (56) is in contact with the side surface (48a) of the idler gear(48). Therefore, as compared to a case where the sleeve (56) is brought into contact with the shift fork (60) to position the sleeve against the thrust force generated due to the inclined tooth surfaces (86, 88), the sliding surface pressure can be reduced between the sleeve (56) and the shift fork (60).