An internal combustion engine comprising: a reciprocating piston; a connecting rod connected to the piston; and a crankshaft connected to the connecting rod; the crankshaft comprising: a first crank web including a first surface, a second surface being an opposite surface to the first surface, and a first hole extending from the first surface to the second surface; a first extension shaft protruding from a center of rotation of the first crank web in the first surface; and a crank pin press-fitted in the first hole, protruding from the second surface of the first crank web, and connected to the connecting rod, wherein: the first surface of the first crank web includes a first inner peripheral edge portion positioned around the first hole, and a first recessed portion recessed relative to the first inner peripheral edge portion (41 B); the second surface of the first crank web includes a first balance weight portion provided opposite the first hole with respect to the center of rotation of the first crank web and protruding from the second surface; and where a direction in which the first hole is positioned with respect to the center of rotation (31 c) of the first crank web is defined as upward or a first direction and a direction in which the first balance weight portion is positioned with respect to the center of rotation of the first crank web is defined as downward or a second direction, an upper end of the first recessed portion is positioned upward relative to, or further from the center of rotation (31 c) of the first crank web in the first direction than, a lower end of the first hole, and a lower end (41 Cb) of the first recessed portion is positioned downward relative to, or further from the center of rotation (31 c) of the first crank web in the second direction than, the lower end of the first hole. a reciprocating piston; a connecting rod connected to the piston; and a crankshaft connected to the connecting rod; the crankshaft comprising: a first crank web including a first surface, a second surface being an opposite surface to the first surface, and a first hole extending from the first surface to the second surface; a first extension shaft protruding from a center of rotation of the first crank web in the first surface; and a crank pin press-fitted in the first hole, protruding from the second surface of the first crank web, and connected to the connecting rod, a first crank web including a first surface, a second surface being an opposite surface to the first surface, and a first hole extending from the first surface to the second surface; a first extension shaft protruding from a center of rotation of the first crank web in the first surface; and a crank pin press-fitted in the first hole, protruding from the second surface of the first crank web, and connected to the connecting rod, the first surface of the first crank web includes a first inner peripheral edge portion positioned around the first hole, and a first recessed portion recessed relative to the first inner peripheral edge portion (41 B); the second surface of the first crank web includes a first balance weight portion provided opposite the first hole with respect to the center of rotation of the first crank web and protruding from the second surface; and where a direction in which the first hole is positioned with respect to the center of rotation (31 c) of the first crank web is defined as upward or a first direction and a direction in which the first balance weight portion is positioned with respect to the center of rotation of the first crank web is defined as downward or a second direction, an upper end of the first recessed portion is positioned upward relative to, or further from the center of rotation (31 c) of the first crank web in the first direction than, a lower end of the first hole, and a lower end (41 Cb) of the first recessed portion is positioned downward relative to, or further from the center of rotation (31 c) of the first crank web in the second direction than, the lower end of the first hole.