A packet detecting device used in a receiver employing PCI Express protocol is disclosed. The packet detecting device includes: a physical layer packet detecting unit for detecting a physical layer packet from a PCI express packet received and parallelized to 16 bit data through a physical deserializer; a descrambling unit for descrambling a physical layer packet from a PCI express packet received and parallelized to 16 bit data through a physical deserializer; a data link layer packet detecting unit for detecting a data link layer packet from a descrambled packet outputted from the descrambling unit; and a transaction layer packet detecting unit for detecting a transaction layer packet from a descrambled packet outputted from the descrambling unit.