An intrusion detection apparatus and method using a load balancer responsive to traffic conditions between a central processing unit (CPU) and a graphics processing unit (GPU) are provided. The intrusion detection apparatus includes a packet acquisition unit, a character string check task allocation unit, a CPU character string check unit, and a GPU character string check unit. The packet acquisition unit receives packets, and stores the packets in a single task queue. The character string check task allocation unit determines the number of packets in the packet acquisition unit, and allocates character string check tasks to the CPU or the GPU. The CPU character string check unit compares the character strings of the packets with a character string defined in at least one detection rule inside the CPU. The GPU character string check unit compares the character strings of the packets with the character string inside the GPU.