The authors developed a novel infant behavior recognition system based on a pressure distribution image. The system can recognize an infant's status (quiet, moving and crying), posture, body parts' positions and movement unrestrainedly. It can, in recognizing the behavior, cope with the infant's rapid growth and unique physique. The algorithm of the infant behavior recognition system is summarized as follows. 1) First, the system measures the pressure distribution image with 384 pressure sensors distributed in the bed. 2) The authors propose "activity score"; this is calculated by using the measured pressure distribution image and indicates kinetic energy of the infant's activity. Based on the activity score, the system decides the infant's status. 3) If the infant is quiet, the system estimates the infant's physique. 4) Based on the estimated physique, the system recognizes the infant's posture and body part movement. Experimental results reveal that the system successfully recognizes infants' status (quiet, moving and crying), posture, body parts position and movements.