Apparatus and method for alarming decrease in tire air-pressure

An apparatus for alarming decrease in tire air-pressure for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a vehicle, comprising:

• a rotational information detecting means for detecting rotational information of the respective tires;
• a rotational information memory means for storing the rotational information of the respective tires;
• a judged value calculating means for calculating judged values based on the rotational information of the respective tires;
• a judged value memory means for storing the judged values;
• a transition calculating means for calculating transition of the judged values based on the stored judged values;
• a judging means for determining a decrease in tire air-pressure based on the judged values;
• and an alarming means for issuing preliminary alarm prior to issuing a predetermined alarm for informing decrease in internal pressure based on the transition of the judged values in case the judged value tends to move to exceed a predetermined threshold for determining a decrease in internal pressure.