A cell culture apparatus having a culture medium replacement function, comprising: a drive chamber (2; 102); an incubator chamber (1; 101) located under the drive chamber (2; 102); a rotatable shaft body; and a rotatable shaft body driving means (11; 111) in the drive chamber (2; 102); wherein at least one set of upper (19; 30; 107) and lower discs (18; 29; 106) each fixed to the rotatable shaft body is horizontally arranged inside the incubator chamber (1; 101), Petri dishes (4; 6; 104) in each of which cells and a culture medium are put are held on the lower disc (18; 29; 106), top lids (5; 7; 105) are held on the upper disc (19; 30; 107) such that it is possible to achieve a state in which the lower disc (18; 29; 106) and the upper disc (19; 30; 107) are brought vertically close to each other to cover the Petri dishes (4; 6; 104) with the top lids (5; 7; 105) and a state in which the lower disc (18; 29; 106) and the upper disc (19; 30; 107) are vertically separated from each other and one of the lower disc (18; 29; 106) and the upper disc (19; 30; 107) is rotated by a predetermined angle to laterally shift the top lids (5; 7; 105) from the Petri dishes (4; 6; 104) so that the Petri dishes (4; 6; 104) are partially exposed, culture medium replacement means (13; 113) is inserted into the exposed portion of a Petri dish (4; 6; 104) from the upper side through an insertion hole (24; 37; 124) formed on the upper disc (19; 30; 107) and the culture medium is replaced, the culture medium replacement means (13; 113) is then retracted, and the lower disc (18; 29; 106) and the upper disc (19; 30; 107) are rotated and vertically displaced to cover the Petri dishes (4; 6; 104) with the top lids (5; 7; 105) to continue cell culture. a drive chamber (2; 102); an incubator chamber (1; 101) located under the drive chamber (2; 102); a rotatable shaft body; and a rotatable shaft body driving means (11; 111) in the drive chamber (2; 102); wherein at least one set of upper (19; 30; 107) and lower discs (18; 29; 106) each fixed to the rotatable shaft body is horizontally arranged inside the incubator chamber (1; 101), Petri dishes (4; 6; 104) in each of which cells and a culture medium are put are held on the lower disc (18; 29; 106), top lids (5; 7; 105) are held on the upper disc (19; 30; 107) such that it is possible to achieve a state in which the lower disc (18; 29; 106) and the upper disc (19; 30; 107) are brought vertically close to each other to cover the Petri dishes (4; 6; 104) with the top lids (5; 7; 105) and a state in which the lower disc (18; 29; 106) and the upper disc (19; 30; 107) are vertically separated from each other and one of the lower disc (18; 29; 106) and the upper disc (19; 30; 107) is rotated by a predetermined angle to laterally shift the top lids (5; 7; 105) from the Petri dishes (4; 6; 104) so that the Petri dishes (4; 6; 104) are partially exposed, culture medium replacement means (13; 113) is inserted into the exposed portion of a Petri dish (4; 6; 104) from the upper side through an insertion hole (24; 37; 124) formed on the upper disc (19; 30; 107) and the culture medium is replaced, the culture medium replacement means (13; 113) is then retracted, and the lower disc (18; 29; 106) and the upper disc (19; 30; 107) are rotated and vertically displaced to cover the Petri dishes (4; 6; 104) with the top lids (5; 7; 105) to continue cell culture.