A railcar axle box includes an axle box main body accommodating a bearing supporting an axle. The axle box main body includes: an inner surface defining an accommodating space accommodating the bearing; a first side surface provided at an outer side of the inner surface and at one car width direction side of a car width direction center of the accommodating space; and a second side surface provided at an outer side of the inner surface and at the other car width direction side of the center. A shortest distance between the first side surface and the car width direction center of the accommodating space and a shortest distance between the second side surface and the center are equal to each other in a car width direction.