A lubrication structure of the present invention is applied to a multi-link piston crank mechanism that has a upper link (3), a lower link (6) and a control link (7). Lubricating oil is supplied in an oil storing portion (21) formed between a pair of upper-pin pin boss portions (12) by a plate member (22) through an oil supply hole (19). By oscillating rotary motion of the upper link side pin boss portion (25) that is provided with an oil groove (29) on an end surface of the upper link side pin boss portion (25), the lubricating oil in the oil storing portion (21) is supplied to an upper pin (4).