A parallel cardan driving system steering bogie for a railcar, the parallel cardan driving system steering bogie comprising: a bogie frame supporting a carbody of a the railcar; first and second axles arranged at front and rear sides in a car longitudinal direction, respectively, and extending along a car width direction; a steering mechanism configured to rotate both the first and second axles relative to the bogie frame to perform steering; first and second electric motors supported by the bogie frame, arranged at the front and rear sides in the car longitudinal direction, respectively, and including first and second output shafts, respectively, the first and second output shafts being parallel to the first and second axles at the time of non-steering; and first and second reducers connected to the first and second axles, respectively; the steering bogie further comprising a first constant velocity ball joint by which the first output shaft is coupled to the first reducer and which follows rotations of the first axle at the time of steering to allow relative displacement between the first output shaft and the first reducer, and a second constant velocity ball joint by which the second output shaft is coupled to the second reducer and which follows rotations of the second axle at the time of the steering to allow relative displacement between the second output shaft and the second reducer; characterized in that each of the first and second constant velocity ball joints includes an inner tube (31, 32) including an outer peripheral surface on which a groove portion (31b, 32b) extending in an axial direction is formed, an outer tube (36, 37) including an inner peripheral surface on which a groove portion (36a, 37a) extending in the axial direction is formed, a ball (34, 35) sandwiched between the groove portion (31b, 32b) of the inner tube (31, 32) and the groove portion (36a, 37a) of the outer tube (36, 37), and a ball retainer (38, 39) arranged between the inner tube (31, 32) and the outer tube (36, 37) and holding the ball (34, 35); and a direction in which the groove portion (31b, 32b) of the inner tube (31, 32) extends and a direction in which the groove portion (36a, 37a) of the outer tube (36, 37) extends are the same as each other. a bogie frame supporting a carbody of a the railcar; first and second axles arranged at front and rear sides in a car longitudinal direction, respectively, and extending along a car width direction; a steering mechanism configured to rotate both the first and second axles relative to the bogie frame to perform steering; first and second electric motors supported by the bogie frame, arranged at the front and rear sides in the car longitudinal direction, respectively, and including first and second output shafts, respectively, the first and second output shafts being parallel to the first and second axles at the time of non-steering; and first and second reducers connected to the first and second axles, respectively; the steering bogie further comprising a first constant velocity ball joint by which the first output shaft is coupled to the first reducer and which follows rotations of the first axle at the time of steering to allow relative displacement between the first output shaft and the first reducer, and a second constant velocity ball joint by which the second output shaft is coupled to the second reducer and which follows rotations of the second axle at the time of the steering to allow relative displacement between the second output shaft and the second reducer; characterized in that each of the first and second constant velocity ball joints includes an inner tube (31, 32) including an outer peripheral surface on which a groove portion (31b, 32b) extending in an axial direction is formed, an outer tube (36, 37) including an inner peripheral surface on which a groove portion (36a, 37a) extending in the axial direction is formed, a ball (34, 35) sandwiched between the groove portion (31b, 32b) of the inner tube (31, 32) and the groove portion (36a, 37a) of the outer tube (36, 37), and a ball retainer (38, 39) arranged between the inner tube (31, 32) and the outer tube (36, 37) and holding the ball (34, 35); and an inner tube (31, 32) including an outer peripheral surface on which a groove portion (31b, 32b) extending in an axial direction is formed, an outer tube (36, 37) including an inner peripheral surface on which a groove portion (36a, 37a) extending in the axial direction is formed, a ball (34, 35) sandwiched between the groove portion (31b, 32b) of the inner tube (31, 32) and the groove portion (36a, 37a) of the outer tube (36, 37), and a ball retainer (38, 39) arranged between the inner tube (31, 32) and the outer tube (36, 37) and holding the ball (34, 35); and a direction in which the groove portion (31b, 32b) of the inner tube (31, 32) extends and a direction in which the groove portion (36a, 37a) of the outer tube (36, 37) extends are the same as each other.