A train interior monitoring method for monitoring an interior of a train and recording information in a monitoring-information recording device that is provided with a temporary image memory and an image memory, the method comprising: a step for obtaining image information by using a camera; a step for, by using the monitoring-information recording device, temporarily recording data containing the image information from the camera in the temporary image memory; a step for, by using the monitoring-information recording device when an event occurs, recording, for a period of time before and after detection of the event, the data containing the image information which has already been recorded in the temporary image memory, in the image memory without processing in order to reduce a file size of the data containing the image information, the period of time being set according to what the event is; a step for, by using the monitoring-information recording device, after a predetermined period of time has elapsed, said predetermined period of time being a period of time long enough to accumulate image information in the temporary image memory and that occupies a half of the recording space of the temporary image memory, a step for processing the data containing the image information, which has been recorded in the temporary image memory, in order to reduce the file size of the data containing the image information, wherein the processed data is data of which recorded time is within the first half of said predetermined period of time, a step for recording the processed data in the image memory, and a step for discarding from the data containing the image information held in the temporary image memory, data of which recorded time is within the first half of the predetermined period of time, which data corresponds to the data of which recorded time is within the first half of the predetermined period of time containing the image information that has been recorded in the image memory. a step for obtaining image information by using a camera; a step for, by using the monitoring-information recording device, temporarily recording data containing the image information from the camera in the temporary image memory; a step for, by using the monitoring-information recording device when an event occurs, recording, for a period of time before and after detection of the event, the data containing the image information which has already been recorded in the temporary image memory, in the image memory without processing in order to reduce a file size of the data containing the image information, the period of time being set according to what the event is; a step for, by using the monitoring-information recording device, after a predetermined period of time has elapsed, said predetermined period of time being a period of time long enough to accumulate image information in the temporary image memory and that occupies a half of the recording space of the temporary image memory, a step for processing the data containing the image information, which has been recorded in the temporary image memory, in order to reduce the file size of the data containing the image information, wherein the processed data is data of which recorded time is within the first half of said predetermined period of time, a step for recording the processed data in the image memory, and a step for discarding from the data containing the image information held in the temporary image memory, data of which recorded time is within the first half of the predetermined period of time, which data corresponds to the data of which recorded time is within the first half of the predetermined period of time containing the image information that has been recorded in the image memory.