A device for detecting sleepiness of a subject driving a vehicle, comprising: a means for detecting an opened/ closed state of an eyelid of the subject; a means for detecting sequentially a time interval between transitions between an opened state and a closed state of the eyelid; a means for computing an eyelid opening/closing characteristic amount successively from time series data of the time intervals between transitions between an opened state and a closed state of the eyelid, a threshold value setting means for setting threshold values for the eyelid opening/closing characteristic amount using the eyelid opening/closing characteristic amount obtained in a predetermined period; a sleepiness judging means for judging and storing in a memory that the subject feels sleepiness when the eyelid opening/closing characteristic amount deviates from a range defined with the threshold values after lapse of the predetermined period; and characterised by a data processing portion for detecting an interruption of driving; wherein the threshold value setting means, in restarting the driving of the vehicle after an interruption of the driving of the vehicle detected by the data processing portion for detecting an interruption of driving, judges that the threshold values are to be reset when sleepiness of the subject is detected before the interruption of the driving of the vehicle, and the threshold value setting means resets the threshold values for the eyelid opening/closing characteristic amount using eyelid opening/closing characteristic amounts obtained in the predetermined period after the restarting of the driving when it is judged that the threshold values are to be reset. a means for detecting an opened/ closed state of an eyelid of the subject; a means for detecting sequentially a time interval between transitions between an opened state and a closed state of the eyelid; a means for computing an eyelid opening/closing characteristic amount successively from time series data of the time intervals between transitions between an opened state and a closed state of the eyelid, a threshold value setting means for setting threshold values for the eyelid opening/closing characteristic amount using the eyelid opening/closing characteristic amount obtained in a predetermined period; a sleepiness judging means for judging and storing in a memory that the subject feels sleepiness when the eyelid opening/closing characteristic amount deviates from a range defined with the threshold values after lapse of the predetermined period; and characterised by a data processing portion for detecting an interruption of driving; wherein the threshold value setting means, in restarting the driving of the vehicle after an interruption of the driving of the vehicle detected by the data processing portion for detecting an interruption of driving, judges that the threshold values are to be reset when sleepiness of the subject is detected before the interruption of the driving of the vehicle, and the threshold value setting means resets the threshold values for the eyelid opening/closing characteristic amount using eyelid opening/closing characteristic amounts obtained in the predetermined period after the restarting of the driving when it is judged that the threshold values are to be reset.