A bearing structure for a multi-link-type piston crank mechanism for an internal combustion engine, wherein: the multi-link-type piston crank mechanism includes: a lower link supported by a crank pin of a crankshaft; an upper link connecting a first end portion of the lower link to a piston pin; and a control link connecting a second end portion of the lower link to an eccentric shaft part of a control shaft; the crankshaft is rotatably supported by a crankshaft bearing part, wherein the crankshaft bearing part is formed by a cylinder block and a main bearing cap; and the control shaft is rotatably supported by a control shaft bearing part, wherein the control shaft bearing part is formed by the main bearing cap and a control shaft bearing cap; characterized in that the crankshaft is rotatably supported by the crankshaft bearing part via half-split main bearing metals; the control shaft is rotatably supported by the control shaft bearing part via half-split control shaft bearing metals; the bearing structure further comprises: an in-block oil passage formed in the cylinder block, and extending from an oil gallery of the cylinder block to the crankshaft bearing part; a first oil hole formed and opened in the main bearing metals, and corresponding to a distal end opening of the in-block oil passage; an oil groove formed to extend circumferentially and entirely in an inner periphery of the main bearing metals, and communicating with the first oil hole; a second oil hole formed and opened in the main bearing metals, and communicating with the oil groove, in a region closer to the main bearing cap; an in-cap oil passage formed in the main bearing cap, and including a first end corresponding to the second oil hole, and including a second end reaching the control shaft bearing part; and a third oil hole formed and opened in the control shaft bearing metals, and corresponding to a distal end opening of the in-cap oil passage. the multi-link-type piston crank mechanism includes: a lower link supported by a crank pin of a crankshaft; an upper link connecting a first end portion of the lower link to a piston pin; and a control link connecting a second end portion of the lower link to an eccentric shaft part of a control shaft; a lower link supported by a crank pin of a crankshaft; an upper link connecting a first end portion of the lower link to a piston pin; and a control link connecting a second end portion of the lower link to an eccentric shaft part of a control shaft; the crankshaft is rotatably supported by a crankshaft bearing part, wherein the crankshaft bearing part is formed by a cylinder block and a main bearing cap; and the control shaft is rotatably supported by a control shaft bearing part, wherein the control shaft bearing part is formed by the main bearing cap and a control shaft bearing cap; characterized in that the crankshaft is rotatably supported by the crankshaft bearing part via half-split main bearing metals; the control shaft is rotatably supported by the control shaft bearing part via half-split control shaft bearing metals; the bearing structure further comprises: an in-block oil passage formed in the cylinder block, and extending from an oil gallery of the cylinder block to the crankshaft bearing part; a first oil hole formed and opened in the main bearing metals, and corresponding to a distal end opening of the in-block oil passage; an oil groove formed to extend circumferentially and entirely in an inner periphery of the main bearing metals, and communicating with the first oil hole; a second oil hole formed and opened in the main bearing metals, and communicating with the oil groove, in a region closer to the main bearing cap; an in-cap oil passage formed in the main bearing cap, and including a first end corresponding to the second oil hole, and including a second end reaching the control shaft bearing part; and a third oil hole formed and opened in the control shaft bearing metals, and corresponding to a distal end opening of the in-cap oil passage. an in-block oil passage formed in the cylinder block, and extending from an oil gallery of the cylinder block to the crankshaft bearing part; a first oil hole formed and opened in the main bearing metals, and corresponding to a distal end opening of the in-block oil passage; an oil groove formed to extend circumferentially and entirely in an inner periphery of the main bearing metals, and communicating with the first oil hole; a second oil hole formed and opened in the main bearing metals, and communicating with the oil groove, in a region closer to the main bearing cap; an in-cap oil passage formed in the main bearing cap, and including a first end corresponding to the second oil hole, and including a second end reaching the control shaft bearing part; and a third oil hole formed and opened in the control shaft bearing metals, and corresponding to a distal end opening of the in-cap oil passage.