A lubrication structure for a four-stroke engine configured to lubricate driving parts by supplying oil stored in an oil tank provided separately from a crank chamber, using pressure fluctuation in the crank chamber, the lubrication structure comprising: a first circulating route configured to supply the oil from the oil tank to the crank chamber and return oil mist generated in the crank chamber to the oil tank; a second circulating route configured to supply the oil mist from the oil tank to a valve operating mechanism and return to the oil tank; a discharge passageway configured to discharge blowby gas contained during circulation of the oil from the second circulating route to a combustion chamber; and a partition wall configured to separate between the crank chamber and the oil tank, wherein: a central part of the partition wall is located vertically above a surface of the oil stored in the oil tank even if an engine body is tilted; an opening A1 of the second circulating route is formed in the central part, the oil mist being supplied from the opening A1; an opening B1 of the first circulating route is formed in the central part of the partition wall, the oil being returned from the opening B1 to the oil tank; characterised in that part of the second circulating route is formed by an elastic tubular part, and an end of the elastic tubular part forms the opening A1 of the second circulating route; a pair of upright walls facing one another is integrally formed with the central part of the partition wall, the elastic tubular part being provided between the pair of upright walls, and a fixing part is placed on the pair of upright walls, the fixing part holding the elastic tubular part and a reed valve with one bolt, and fixing an end of the reed valve provided in the opening B1; and the pair of upright walls are configured to be connected by a plurality of connection walls and the elastic tubular part is fixed by the plurality of connection walls. a first circulating route configured to supply the oil from the oil tank to the crank chamber and return oil mist generated in the crank chamber to the oil tank; a second circulating route configured to supply the oil mist from the oil tank to a valve operating mechanism and return to the oil tank; a discharge passageway configured to discharge blowby gas contained during circulation of the oil from the second circulating route to a combustion chamber; and a partition wall configured to separate between the crank chamber and the oil tank, a central part of the partition wall is located vertically above a surface of the oil stored in the oil tank even if an engine body is tilted; an opening A1 of the second circulating route is formed in the central part, the oil mist being supplied from the opening A1; an opening B1 of the first circulating route is formed in the central part of the partition wall, the oil being returned from the opening B1 to the oil tank; characterised in that part of the second circulating route is formed by an elastic tubular part, and an end of the elastic tubular part forms the opening A1 of the second circulating route; a pair of upright walls facing one another is integrally formed with the central part of the partition wall, the elastic tubular part being provided between the pair of upright walls, and a fixing part is placed on the pair of upright walls, the fixing part holding the elastic tubular part and a reed valve with one bolt, and fixing an end of the reed valve provided in the opening B1; and the pair of upright walls are configured to be connected by a plurality of connection walls and the elastic tubular part is fixed by the plurality of connection walls.