A metabolic energy monitoring system is provided which comprises: a wearable device having a movement sensor, a temperature sensor and a pulse wave sensor and adapted to be worn on a human body; a database to store activity state decision knowledge data including activity state decision condition data and calorie consumption calculation knowledge data including a calorie consumption calculating algorithm for each metabolic state; an activity state decision unit to determine the activity state based on a detection signal from the wearable device and activity state decision knowledge data; a metabolic state decision unit to detect an activity continuation state, and determine the metabolic state; a calorie consumption calculating unit to calculate a calorie consumption according to the metabolic state; and an output unit to output the calorie consumption.