A child safety seat , comprising a seat body and a collapsible support device , which is installed on the child safety seat , wherein the collapsible support device comprises a first supporting part and a second supporting part , the second supporting part being pivotally connected to an end of the first supporting part to be capable of being collapsed to the first supporting part , another end of the first supporting part being pivotally connected to the child safety seat , the first supporting part being selectively rotated relative to the child safety seat to be located at one of a use position, where the first supporting part protrudes out the seat body , and a storage position, where the first supporting part is stored in the seat body , the second supporting part being selectively rotated relative to the first supporting part to be located at one of a supporting position and a collapsed position, wherein the collapsible support device further comprises another one of the first supporting part , the two first supporting parts being disposed at two opposite sides of the second supporting part , wherein, when the first supporting part is located at the use position, the child safety seat is at a first forward use state, wherein, when the first supporting part is located at the storage position, the child safety seat is at a rearward use state, and wherein the collapsible support device further comprises a limitation part and a rotation part , the rotation part rotatably passing through the second supporting part , the rotation part and the first supporting part being fixedly connected, an end of the limitation part being inserted into the first supporting part , another end of the limitation part extending into the second supporting part , the second supporting part having a rotation room for the limitation part to extend into, the second supporting part having at least one positioning protrusion , a first positioning area and a second positioning area being formed between the positioning protrusion and a sidewall of the rotation room , when the second supporting part is rotated to locate the limitation part in the first positioning area , the second supporting part being located at the supporting position, when the second supporting part is rotated to locate the limitation part in the second positioning area , the second supporting part being located at the collapsed position. wherein the collapsible support device further comprises another one of the first supporting part , the two first supporting parts being disposed at two opposite sides of the second supporting part , wherein, when the first supporting part is located at the use position, the child safety seat is at a first forward use state, wherein, when the first supporting part is located at the storage position, the child safety seat is at a rearward use state, and wherein the collapsible support device further comprises a limitation part and a rotation part , the rotation part rotatably passing through the second supporting part , the rotation part and the first supporting part being fixedly connected, an end of the limitation part being inserted into the first supporting part , another end of the limitation part extending into the second supporting part , the second supporting part having a rotation room for the limitation part to extend into, the second supporting part having at least one positioning protrusion , a first positioning area and a second positioning area being formed between the positioning protrusion and a sidewall of the rotation room , when the second supporting part is rotated to locate the limitation part in the first positioning area , the second supporting part being located at the supporting position, when the second supporting part is rotated to locate the limitation part in the second positioning area , the second supporting part being located at the collapsed position. <EOS>