The variable length connecting rod 6 comprises: a connecting rod body 31; an eccentric member 32 which can swivel with respect to the connecting rod body and in which the effective length of the variable length connecting rod is changed when swiveled; a first piston mechanism 33 making the eccentric member swivel in one direction when hydraulic fluid is fed; a second piston mechanism 34 making the eccentric member swivel in the opposite direction when hydraulic fluid is fed; and a flow direction changing mechanism 35 switching flow directions of hydraulic fluid between the first piston mechanism 33 and the second piston mechanism 34. The first piston mechanism and second piston mechanism are formed so that a first cylinder volume defined by a stroke length of the first piston and a cross-sectional area of the first cylinder is equal to a second cylinder volume defined by a stroke length of the second piston and a cross-sectional area of the second cylinder.