An engine block, comprising: a cylinder portion in which a plurality of cylinders are arranged in-line; a crankcase portion connected to one end side of the cylinder portion in a cylinder axial direction to form a crank chamber; a transmission attaching portion (26, 50) provided on one end side of the cylinder portion and the crankcase portion in a cylinder row direction; and an oil pan attaching portion extending along the cylinder row direction at an end portion opposite to the side on which the cylinder portion is connected, and formed in a flange-like shape projecting in a direction orthogonal to the cylinder row direction and the cylinder axial direction, wherein the crankcase portion includes supporting walls that rotatably support a crankshaft and are configured to function as a rigidity improving portion capable of improving rigidity thereof, the oil pan attaching portion includes a first portion extending closer to the transmission attaching portion and connected to the transmission attaching portion, and a second portion extending away from the transmission attaching portion farther than first portion, and the oil pan attaching portion is configured such that a second moment of area of a cross-section of the first portion is larger than a second moment of area of a cross-section of the second portion, each of the cross-sections being perpendicular to the cylinder row direction, the oil pan attaching portion has at least one of: a first configuration in which a height of the cross-section of the first portion is higher than a height of the cross-section of the second portion, each of the cross-sections being perpendicular to the cylinder row direction; and a second configuration in which the first portion is formed so that a width gradually increases toward a connecting portion connected to the transmission attaching portion from a connecting portion connected to the second portion, characterized in that the first portion is connected to the supporting wall that has rigidity larger than the rigidity of the other supporting walls, at an end portion opposite to the connecting portion connected to the transmission attaching portion. a cylinder portion in which a plurality of cylinders are arranged in-line; a crankcase portion connected to one end side of the cylinder portion in a cylinder axial direction to form a crank chamber; a transmission attaching portion (26, 50) provided on one end side of the cylinder portion and the crankcase portion in a cylinder row direction; and an oil pan attaching portion extending along the cylinder row direction at an end portion opposite to the side on which the cylinder portion is connected, and formed in a flange-like shape projecting in a direction orthogonal to the cylinder row direction and the cylinder axial direction, wherein the crankcase portion includes supporting walls that rotatably support a crankshaft and are configured to function as a rigidity improving portion capable of improving rigidity thereof, the oil pan attaching portion includes a first portion extending closer to the transmission attaching portion and connected to the transmission attaching portion, and a second portion extending away from the transmission attaching portion farther than first portion, and the oil pan attaching portion is configured such that a second moment of area of a cross-section of the first portion is larger than a second moment of area of a cross-section of the second portion, each of the cross-sections being perpendicular to the cylinder row direction, the oil pan attaching portion has at least one of: a first configuration in which a height of the cross-section of the first portion is higher than a height of the cross-section of the second portion, each of the cross-sections being perpendicular to the cylinder row direction; and a second configuration in which the first portion is formed so that a width gradually increases toward a connecting portion connected to the transmission attaching portion from a connecting portion connected to the second portion, a first configuration in which a height of the cross-section of the first portion is higher than a height of the cross-section of the second portion, each of the cross-sections being perpendicular to the cylinder row direction; and a second configuration in which the first portion is formed so that a width gradually increases toward a connecting portion connected to the transmission attaching portion from a connecting portion connected to the second portion, characterized in that the first portion is connected to the supporting wall that has rigidity larger than the rigidity of the other supporting walls, at an end portion opposite to the connecting portion connected to the transmission attaching portion.