This invention provides a support carriage that carries and supports a grass collecting device when the grass collecting device is attached to and detached from the rear portion of a vehicle body, and a riding grass mower that has the support carriage. A support carriage (C) includes a base portion (30) that can move over a work floor (G), and a positioning portion (42) that is provided in the front portion of the base portion (30) and can be engaged with the vehicle body from behind. When the positioning portion (42) is engaged with the vehicle body, the base portion (30) is positioned relative to the vehicle body in the front-rear direction and the width direction.
