A single-cylinder internal-combustion engine comprising: a crankshaft including a first part formed by integrally forming a first crank web, a crank pin that extends from the first crank web, and a first shaft that is arranged in an opposite side to the crank pin with respect to the first crank web and extends from the first crank web, and a second part formed by integrally forming a second crank web in which a pin hole in which the crank pin of the first part is pressed is formed, and a second shaft that is arranged in an opposite side to the first crank web with respect to the second crank web and extends from the second crank web, wherein, in the first part, an oil passage that passes inside the crank pin and inside the first crank web and has an outlet port and an inlet port is formed, the oil passage is formed of an inclined passage that is inclined with respect to the axis of the first shaft, when viewed from a direction that is perpendicular to a plane including an axis of the crank pin and an axis of the first shaft, the oil passage has a passage portion that overlaps the axis of the first shaft, and the single-cylinder internal-combustion engine includes a connecting rod which has a large end portion in which a hole in which the crank pin is inserted is formed and in which at least a peripheral portion of the hole of the large end portion is integrally formed, and a bearing that is arranged inside the hole of the large end portion of the connecting rod and exists between the large end portion of the connecting rod and the crank pin, the bearing is a sliding bearing, wherein the first shaft includes a journal portion, the internal-combustion engine includes another sliding bearing that rotatably supports the journal portion, characterized in that the oil passage that passes inside the crank pin and inside the first crank web and has the outlet port formed in an outer peripheral surface of the crank pin, wherein the inlet port of the oil passage is formed in an outer peripheral surface of the first shaft, and the inlet port of the oil passage is formed in the outer peripheral surface of the journal portion. a crankshaft including a first part formed by integrally forming a first crank web, a crank pin that extends from the first crank web, and a first shaft that is arranged in an opposite side to the crank pin with respect to the first crank web and extends from the first crank web, and a second part formed by integrally forming a second crank web in which a pin hole in which the crank pin of the first part is pressed is formed, and a second shaft that is arranged in an opposite side to the first crank web with respect to the second crank web and extends from the second crank web, wherein, in the first part, an oil passage that passes inside the crank pin and inside the first crank web and has an outlet port and an inlet port is formed, the oil passage is formed of an inclined passage that is inclined with respect to the axis of the first shaft, when viewed from a direction that is perpendicular to a plane including an axis of the crank pin and an axis of the first shaft, the oil passage has a passage portion that overlaps the axis of the first shaft, and the single-cylinder internal-combustion engine includes a connecting rod which has a large end portion in which a hole in which the crank pin is inserted is formed and in which at least a peripheral portion of the hole of the large end portion is integrally formed, and a bearing that is arranged inside the hole of the large end portion of the connecting rod and exists between the large end portion of the connecting rod and the crank pin, the bearing is a sliding bearing, wherein the first shaft includes a journal portion, a connecting rod which has a large end portion in which a hole in which the crank pin is inserted is formed and in which at least a peripheral portion of the hole of the large end portion is integrally formed, and a bearing that is arranged inside the hole of the large end portion of the connecting rod and exists between the large end portion of the connecting rod and the crank pin, the bearing is a sliding bearing, wherein the first shaft includes a journal portion, the internal-combustion engine includes another sliding bearing that rotatably supports the journal portion, characterized in that the oil passage that passes inside the crank pin and inside the first crank web and has the outlet port formed in an outer peripheral surface of the crank pin, wherein the inlet port of the oil passage is formed in an outer peripheral surface of the first shaft, and the inlet port of the oil passage is formed in the outer peripheral surface of the journal portion.