A crankshaft for a reciprocating engine, the crankshaft comprising: journals that define a central axis of rotation (Jc); crank pins that are eccentric with respect to the journals; crank arms connecting the journals to the crank pins; and counterweights integrated with the crank arms, wherein when the crankshaft is mounted in the reciprocating engine, a load due to combustion pressure is applied to each of the crank pins via a connecting rod in a direction from an axis of a piston pin to an axis (Pc) of the crank pin; wherein each of the crank arms has an asymmetric shape with respect to a crank arm centerline (Ac), the crank arm centerline (Ac) corresponding to a line on a plane connecting the axis (Pc) of the crank pin to an axis (Jc) of the journal when viewed in an axial direction; wherein each of the crank arms has a maximum flexural rigidity when the load applied onto the crank pin due to the combustion pressure is a maximum load (Fmax) in the direction inclined at the maximum load angle (α) from the crank arm centerline (Ac); and wherein when each of the crank arms is divided by the crank arm centerline (Ac) into a left arm portion (Af) that is the side subjected to the maximum load (Fmax) and a right arm portion ('Ar) opposite to the side that is subjected to the maximum load (Fmax), in each section of each of the crank arms on a plane perpendicular to the crank arm centerline (Ac) at a position outward of the axis (Pc) of the crank pin, an area moment of inertia of the left arm portion (Af) is greater than an area moment of inertia of the right arm portion (Ar), and in each section of each of the crank arms on a plane perpendicular to the crank arm centerline (Ac) at a position inward of the axis (Pc) of the crank pin, the area moment of inertia of the right arm portion (Ar) is greater than the area moment of inertia of the left arm portion (Af). journals that define a central axis of rotation (Jc); crank pins that are eccentric with respect to the journals; crank arms connecting the journals to the crank pins; and counterweights integrated with the crank arms, wherein when the crankshaft is mounted in the reciprocating engine, a load due to combustion pressure is applied to each of the crank pins via a connecting rod in a direction from an axis of a piston pin to an axis (Pc) of the crank pin; wherein each of the crank arms has an asymmetric shape with respect to a crank arm centerline (Ac), the crank arm centerline (Ac) corresponding to a line on a plane connecting the axis (Pc) of the crank pin to an axis (Jc) of the journal when viewed in an axial direction; wherein each of the crank arms has a maximum flexural rigidity when the load applied onto the crank pin due to the combustion pressure is a maximum load (Fmax) in the direction inclined at the maximum load angle (α) from the crank arm centerline (Ac); and wherein when each of the crank arms is divided by the crank arm centerline (Ac) into a left arm portion (Af) that is the side subjected to the maximum load (Fmax) and a right arm portion ('Ar) opposite to the side that is subjected to the maximum load (Fmax), in each section of each of the crank arms on a plane perpendicular to the crank arm centerline (Ac) at a position outward of the axis (Pc) of the crank pin, an area moment of inertia of the left arm portion (Af) is greater than an area moment of inertia of the right arm portion (Ar), and in each section of each of the crank arms on a plane perpendicular to the crank arm centerline (Ac) at a position inward of the axis (Pc) of the crank pin, the area moment of inertia of the right arm portion (Ar) is greater than the area moment of inertia of the left arm portion (Af).