A lifting apparatus capable of engaging with and disengaging from a water treatment device which is to be lifted, the lifting apparatus comprising: a frame having two side portions each provided with an engaging portion pivotably attached to the frame by an upper portion thereof in a vertical position, each engaging portion being capable of engaging with an engageable portion of the water treatment device, wherein each engaging portion has a first operation state in which the engaging portion pivots by contacting the engageable portion of the water treatment device as the lifting apparatus approaches the water treatment device from above, and then pivots back to the vertical position as the lifting apparatus further approaches the water treatment device to become closer thereto, whereby each engaging portion and the engageable portion of the water treatment device become engageable with each other, and wherein each engaging portion has a second operation state in addition to the first operation state, in which the engaging portion disengages from the engageable portion by a weight thereof or a biased force, when the lifting apparatus further approaches the water treatment device after the water treatment device has been installed into a predetermined position from a lifted state thereof being lifted by the lifting apparatus, characterized in that the frame has a pair of holes (47, 48) with an outer-side hole and an inner-side hole on each of the two side portion thereof, and the first operation state and the second operation state are switched by changing a position by changing the hole of the pair of holes (47, 48) to which the engaging portions are attached to the frame, or by attaching and releasing one end of a biasing means to each of the engaging portions while the engaging portions are attached to one hole of the pair of holes (47, 48) and the other end of biasing means is attached to the other hole of the pair of holes (47, 48). a frame having two side portions each provided with an engaging portion pivotably attached to the frame by an upper portion thereof in a vertical position, each engaging portion being capable of engaging with an engageable portion of the water treatment device, wherein each engaging portion has a first operation state in which the engaging portion pivots by contacting the engageable portion of the water treatment device as the lifting apparatus approaches the water treatment device from above, and then pivots back to the vertical position as the lifting apparatus further approaches the water treatment device to become closer thereto, whereby each engaging portion and the engageable portion of the water treatment device become engageable with each other, and wherein each engaging portion has a second operation state in addition to the first operation state, in which the engaging portion disengages from the engageable portion by a weight thereof or a biased force, when the lifting apparatus further approaches the water treatment device after the water treatment device has been installed into a predetermined position from a lifted state thereof being lifted by the lifting apparatus, characterized in that the frame has a pair of holes (47, 48) with an outer-side hole and an inner-side hole on each of the two side portion thereof, and the first operation state and the second operation state are switched by changing a position by changing the hole of the pair of holes (47, 48) to which the engaging portions are attached to the frame, or by attaching and releasing one end of a biasing means to each of the engaging portions while the engaging portions are attached to one hole of the pair of holes (47, 48) and the other end of biasing means is attached to the other hole of the pair of holes (47, 48). by changing a position by changing the hole of the pair of holes (47, 48) to which the engaging portions are attached to the frame, or by attaching and releasing one end of a biasing means to each of the engaging portions while the engaging portions are attached to one hole of the pair of holes (47, 48) and the other end of biasing means is attached to the other hole of the pair of holes (47, 48).