A synthetic resin-made sliding bearing comprising: a synthetic resin-made upper casing having a cylindrical outer peripheral side surface; a synthetic resin-made lower casing which has a cylindrical inner peripheral side surface opposed to the outer peripheral side surface of said upper casing in a radial direction so as to surround the outer peripheral side surface of said upper casing with a cylindrical fitting clearance extending in such a manner as to intersect the radial direction, and on which said upper casing is mounted as said upper casing is fitted thereto such that a radial displacement of said lower casing with respect to said upper casing is made possible with a radial minimum width of the fitting clearance by being restricted by the contact of the inner peripheral side surface with the outer peripheral side surface of said upper casing; and a synthetic resin-made thrust sliding bearing disposed in an annular space between said upper casing and said lower casing in a vertical direction, characterized in that in an outer peripheral side clearance allowing a radially outer peripheral portion of the annular space to communicate with an outside of the synthetic resin-made sliding bearing and constituted by mutually opposing surfaces of said upper casing and said lower casing, a clearance extending in such a manner as to intersect the radial direction has a radial width which is equal to or greater than the radial minimum width of the fitting clearance and in an inner peripheral side clearance allowing a radially inner peripheral portion of the annular space to communicate with the outside of the synthetic resin-made sliding bearing through the fitting clearance and constituted by mutually opposing surfaces of said upper casing and said lower casing, a clearance extending in such a manner as to intersect the radial direction has a radial width which is equal to or greater than the radial minimum width of the fitting clearance. a synthetic resin-made upper casing having a cylindrical outer peripheral side surface; a synthetic resin-made lower casing which has a cylindrical inner peripheral side surface opposed to the outer peripheral side surface of said upper casing in a radial direction so as to surround the outer peripheral side surface of said upper casing with a cylindrical fitting clearance extending in such a manner as to intersect the radial direction, and on which said upper casing is mounted as said upper casing is fitted thereto such that a radial displacement of said lower casing with respect to said upper casing is made possible with a radial minimum width of the fitting clearance by being restricted by the contact of the inner peripheral side surface with the outer peripheral side surface of said upper casing; and a synthetic resin-made thrust sliding bearing disposed in an annular space between said upper casing and said lower casing in a vertical direction, characterized in that in an outer peripheral side clearance allowing a radially outer peripheral portion of the annular space to communicate with an outside of the synthetic resin-made sliding bearing and constituted by mutually opposing surfaces of said upper casing and said lower casing, a clearance extending in such a manner as to intersect the radial direction has a radial width which is equal to or greater than the radial minimum width of the fitting clearance and in an inner peripheral side clearance allowing a radially inner peripheral portion of the annular space to communicate with the outside of the synthetic resin-made sliding bearing through the fitting clearance and constituted by mutually opposing surfaces of said upper casing and said lower casing, a clearance extending in such a manner as to intersect the radial direction has a radial width which is equal to or greater than the radial minimum width of the fitting clearance.