A planetary bearing structure which does not require forcible oil supply of planetary bearing using slide bearing, and which can reliably supply oil to a sliding surface and lubricate the sliding surface with a simple structure. The planetary bearing structure including: a planetary pin (30) fixed to a carrier (21), and a planetary gear (40) having a slide bearing (50) mounted on an inner peripheral surface of a shaft hole (40a), in which the planetary pin (30) turnably supports the planetary gear (40) through the slide bearing (50), and both end surfaces (41L, 41R) of the planetary gear (40) form a pair of gaps (SL, SR) between opposed wall surfaces (21L, 21R) of the carrier (21) and rotate, wherein a pair of spiral grooves (42L, 42R) formed in one of the gear end surfaces (41, 41R) forming the pair of gaps (SL, SR) and the opposed wall surfaces (21L, 21R) and oppositely oriented at gaps (SL, SR), and the planetary bearing structure has such a lubricant oil passage that the gaps (SL, SR) take an oil bath in lubricant oil, lubricant oil introduced from the sucking side gap (SR) passes between the planetary pin (30) and the slide bearing (50) and is discharged from the other discharging side gap (SL).