In order to objectively grasp a stress state of a user and to prevent postpartum depression, biological gas information is acquired via a network, where the biological gas information indicates a concentration of 2-ethyl-1-hexanol of the user and is obtained by a sensor that detects 2-ethyl-1-hexanol released from a skin surface of the user. From a memory storing information including an upper limit of a normal range of the concentration of 2-ethyl-1-hexanol per unit period, the information indicating the upper limit of the normal range is read out. When a frequency in the unit period with which the concentration of 2-ethyl-1-hexanol of the user exceeds the upper limit of the normal range is determined to have an increasing tendency based on the biological gas information obtained during a pregnancy period of the user, the information related to stress of the user is output to an information terminal of the user.