In a differential locking mechanism, a first differential side gear is fixed on a first axle, a second differential side gear is fixed on a second axle, and a bull gear including an engagement part is disposed between the first and second side gears. A cylindrical part is provided on the first differential side gear unrotatably relative to the first differential side gear, and includes a circumferential portion surrounding the first differential side gear. A differential locking slider is fitted on the circumferential portion of the cylindrical part unrotatably relative to the cylindrical part and axially slidably. The differential locking slider is slidable in a direction to engage its engagement part with the engagement part of the bull gear, and in another direction to disengage its engagement part from the engagement part of the bull gear.