An engine for a straddled vehicle comprising: a camshaft; a cam chain coupled to the camshaft; a cylinder head made of metal, the cylinder head including a cam support portion (211,221) supporting the camshaft and a cam chain compartment in which the cam chain is disposed; and a head cover being attached to the cylinder head, wherein the cylinder head includes a mating surface to be attached to the head cover, the mating surface includes a first mating surface portion, a second mating surface portion, a third mating surface portion and a fourth mating surface portion, the first mating surface portion is adjacent to the cam chain compartment, the third mating surface portion is located on an opposite side of the first mating surface portion, the second mating surface portion connects the first mating surface portion and the third mating surface portion, the fourth mating surface portion is located on an opposite side of the second mating surface portion, the fourth mating surface portion connects the first mating surface portion and the third mating surface portion, and where in a cylinder axial direction of the cylinder head, a directional side from the head cover to the cylinder head is defined as downward and a directional side from the cylinder head to the head cover is defined as upward, at least portion of the first mating surface portion is located downward of a lower end of the cam support portion (211,221), and at least portion of the second mating surface portion, at least portion of the third mating surface portion and at least portion of the fourth mating surface portion are located upward of the lower end of the cam support portion (211,221), characterized in that the head cover is made of resin, the head cover includes a chain restraining portion, the chain restraining portion sticks out from the inner surface of the head cover, the chain restraining portion extends to a position lateral to the cam chain, and the chain restraining portion has a thickness smaller than an interval between a pair of plates of the cam chain or a width of a bushing of the cam chain. a camshaft; a cam chain coupled to the camshaft; a cylinder head made of metal, the cylinder head including a cam support portion (211,221) supporting the camshaft and a cam chain compartment in which the cam chain is disposed; and a head cover being attached to the cylinder head, wherein the cylinder head includes a mating surface to be attached to the head cover, the mating surface includes a first mating surface portion, a second mating surface portion, a third mating surface portion and a fourth mating surface portion, the first mating surface portion is adjacent to the cam chain compartment, the third mating surface portion is located on an opposite side of the first mating surface portion, the second mating surface portion connects the first mating surface portion and the third mating surface portion, the fourth mating surface portion is located on an opposite side of the second mating surface portion, the fourth mating surface portion connects the first mating surface portion and the third mating surface portion, and where in a cylinder axial direction of the cylinder head, a directional side from the head cover to the cylinder head is defined as downward and a directional side from the cylinder head to the head cover is defined as upward, at least portion of the first mating surface portion is located downward of a lower end of the cam support portion (211,221), and at least portion of the second mating surface portion, at least portion of the third mating surface portion and at least portion of the fourth mating surface portion are located upward of the lower end of the cam support portion (211,221), characterized in that the head cover is made of resin, the head cover includes a chain restraining portion, the chain restraining portion sticks out from the inner surface of the head cover, the chain restraining portion extends to a position lateral to the cam chain, and the chain restraining portion has a thickness smaller than an interval between a pair of plates of the cam chain or a width of a bushing of the cam chain.