A device for predicting thyrotoxicosis of a user subject to a treatment for improving a thyroid function, the device including: a communication module configured to receive data from an external device and transmit data to an external device; a memory configured to store the data; and a computing unit, wherein the computing unit is configured to: receive bio-signals of the user from an external device, and thus, receive plural heart rates for the user from an external device, wherein each of the plural heart rates is classified into i) resting heart rate of awake period, ii) resting heart rate of sleep period, extract a section in which the number of steps is 0 for a predetermined period of time in a day from data obtained by measuring the number of steps of a patient and calculate a median value of a plurality of heart rates measured in each section determine a reference resting heart rate for the user corresponding to plural reference days based on calculating an average of resting heart rates for a pre-determined number of days during which a thyroid function is normal which are obtained with respect to the plural reference days, wherein resting periods are respectively periods with zero steps, obtain, with respect to plural current days, plural current day representative values of resting heart rates based on calculating a representative value per corresponding day, wherein the representative value per corresponding day is a median value of the obtained resting heart rates per corresponding day, wherein greater weight is assigned to the sleep period than to the awake period, and output, through an output unit of a measuring device, an alert to the user when it is determined that the current resting heart rate of a predetermined number of consecutive days is greater than the reference heart rate based on a predetermined value. a communication module configured to receive data from an external device and transmit data to an external device; a memory configured to store the data; and a computing unit, wherein the computing unit is configured to: receive bio-signals of the user from an external device, and thus, receive plural heart rates for the user from an external device, wherein each of the plural heart rates is classified into i) resting heart rate of awake period, ii) resting heart rate of sleep period, extract a section in which the number of steps is 0 for a predetermined period of time in a day from data obtained by measuring the number of steps of a patient and calculate a median value of a plurality of heart rates measured in each section determine a reference resting heart rate for the user corresponding to plural reference days based on calculating an average of resting heart rates for a pre-determined number of days during which a thyroid function is normal which are obtained with respect to the plural reference days, wherein resting periods are respectively periods with zero steps, obtain, with respect to plural current days, plural current day representative values of resting heart rates based on calculating a representative value per corresponding day, wherein the representative value per corresponding day is a median value of the obtained resting heart rates per corresponding day, wherein greater weight is assigned to the sleep period than to the awake period, and output, through an output unit of a measuring device, an alert to the user when it is determined that the current resting heart rate of a predetermined number of consecutive days is greater than the reference heart rate based on a predetermined value. receive bio-signals of the user from an external device, and thus, receive plural heart rates for the user from an external device, wherein each of the plural heart rates is classified into i) resting heart rate of awake period, ii) resting heart rate of sleep period, extract a section in which the number of steps is 0 for a predetermined period of time in a day from data obtained by measuring the number of steps of a patient and calculate a median value of a plurality of heart rates measured in each section determine a reference resting heart rate for the user corresponding to plural reference days based on calculating an average of resting heart rates for a pre-determined number of days during which a thyroid function is normal which are obtained with respect to the plural reference days, wherein resting periods are respectively periods with zero steps, obtain, with respect to plural current days, plural current day representative values of resting heart rates based on calculating a representative value per corresponding day, wherein the representative value per corresponding day is a median value of the obtained resting heart rates per corresponding day, wherein greater weight is assigned to the sleep period than to the awake period, and output, through an output unit of a measuring device, an alert to the user when it is determined that the current resting heart rate of a predetermined number of consecutive days is greater than the reference heart rate based on a predetermined value.