A shaft assembly device, the shaft assembly comprising a plurality of pistons each installed on a swash plate via a pair of shoes matching with a pair of end surfaces of the swash plate, respectively, the assembly device comprising: a shaft support portion for supporting a shaft having the swash plate, whereby said shaft is in a vertical axis posture; a guide member equipped with a first guide surface and a second guide surface, for guiding each piston of the plurality of pistons to the swash plate to match the pair of the shoes with the pair of end surfaces of the swash plate respectively, while holding one shoe of the pair of shoes. in slidable contact with the first guide surface and another shoe of the pair of shoes in slidable contact with the second guide surface; conveyance means for conveying the plurality of pistons guided by the guide member, whereby said plurality of pistons are in the vertical axis posture; and a piston holding portion for holding the plurality of pistons guided to the swash plate at circumferentially equidistant positions of the swash plate, respectively, whereby said plurality of pistons are in the vertical axis posture; the shaft assembly device characterised by: a shoe incorporation mechanism for inserting the pair of the shoes between each piston of the plurality of pistons and the first guide surface and between said each piston of the plurality of pistons and the second guide surface, respectively; wherein the shoe incorporation mechanism, is equipped with a groove portion provided in at least one guide surface of the first and second guide surfaces (22, 23) and an elastic member disposed on a groove bottom surface of the groove portion and elastically deformable in a direction so as to increase a groove depth, said shoe incorporation mechanism adapted to insert one shoe of the pair of shoes which is supplied to the groove portion with the groove depth reduced between said at least one guide surface of the first and second guide surfaces (22, 23) and a corresponding piston of the plurality of pistons while elastically deforming the elastic member. a shaft support portion for supporting a shaft having the swash plate, whereby said shaft is in a vertical axis posture; a guide member equipped with a first guide surface and a second guide surface, for guiding each piston of the plurality of pistons to the swash plate to match the pair of the shoes with the pair of end surfaces of the swash plate respectively, while holding one shoe of the pair of shoes. in slidable contact with the first guide surface and another shoe of the pair of shoes in slidable contact with the second guide surface; conveyance means for conveying the plurality of pistons guided by the guide member, whereby said plurality of pistons are in the vertical axis posture; and a piston holding portion for holding the plurality of pistons guided to the swash plate at circumferentially equidistant positions of the swash plate, respectively, whereby said plurality of pistons are in the vertical axis posture; the shaft assembly device characterised by: a shoe incorporation mechanism for inserting the pair of the shoes between each piston of the plurality of pistons and the first guide surface and between said each piston of the plurality of pistons and the second guide surface, respectively; wherein the shoe incorporation mechanism, is equipped with a groove portion provided in at least one guide surface of the first and second guide surfaces (22, 23) and an elastic member disposed on a groove bottom surface of the groove portion and elastically deformable in a direction so as to increase a groove depth, said shoe incorporation mechanism adapted to insert one shoe of the pair of shoes which is supplied to the groove portion with the groove depth reduced between said at least one guide surface of the first and second guide surfaces (22, 23) and a corresponding piston of the plurality of pistons while elastically deforming the elastic member. a shoe incorporation mechanism for inserting the pair of the shoes between each piston of the plurality of pistons and the first guide surface and between said each piston of the plurality of pistons and the second guide surface, respectively; wherein the shoe incorporation mechanism, is equipped with a groove portion provided in at least one guide surface of the first and second guide surfaces (22, 23) and an elastic member disposed on a groove bottom surface of the groove portion and elastically deformable in a direction so as to increase a groove depth, said shoe incorporation mechanism adapted to insert one shoe of the pair of shoes which is supplied to the groove portion with the groove depth reduced between said at least one guide surface of the first and second guide surfaces (22, 23) and a corresponding piston of the plurality of pistons while elastically deforming the elastic member.