A variable compression ratio apparatus includes: a piston defining a combustion chamber, a connecting rod connected to the piston; an eccentric link eccentrically connected to the piston, a swing link connected to the eccentric link so as to rotate the eccentric link, a crankpin to which the connecting rod is connected, and a crank web disposed at both sides of the crankpin and provided with a guide portion for guiding downward motions of the eccentric link and the swing link when the eccentric link and the swing link move downward. Thereby, the downward motions of the eccentric link and the swing link are stabilized.