A dryer comprising: a drum; a wireless sensing device disposed in and configured to move freely around the drum and comprising: a sensing module including a humidity sensor configured to measure humidity in the drum, and an acceleration sensor, a sensor communication module configured to transmit or receive data through wireless communication, a sensor controller configured to control the sensor communication module to transmit a humidity value corresponding to an output of the humidity sensor, and a sensor power supplier configured to supply power to the sensing module, the sensor communication module, and the sensor controller; a main communication module configured to receive the humidity value from the wireless sensing device; and a main controller configured to determine that drying is completed when the humidity value is equal to or less than a set threshold, wherein the acceleration sensor is configured to measure acceleration while being rotated along with the drum, wherein the sensor controller is configured to control the sensor communication module to transmit an acceleration value corresponding to an output of the acceleration sensor, and wherein the main controller is configured to determine at least one of a load of laundry contained in the drum, or determine whether laundry contained in the drum is entangled, based on the acceleration value. a drum; a wireless sensing device disposed in and configured to move freely around the drum and comprising: a sensing module including a humidity sensor configured to measure humidity in the drum, and an acceleration sensor, a sensor communication module configured to transmit or receive data through wireless communication, a sensor controller configured to control the sensor communication module to transmit a humidity value corresponding to an output of the humidity sensor, and a sensor power supplier configured to supply power to the sensing module, the sensor communication module, and the sensor controller; a sensing module including a humidity sensor configured to measure humidity in the drum, and an acceleration sensor, a sensor communication module configured to transmit or receive data through wireless communication, a sensor controller configured to control the sensor communication module to transmit a humidity value corresponding to an output of the humidity sensor, and a sensor power supplier configured to supply power to the sensing module, the sensor communication module, and the sensor controller; a main communication module configured to receive the humidity value from the wireless sensing device; and a main controller configured to determine that drying is completed when the humidity value is equal to or less than a set threshold, wherein the acceleration sensor is configured to measure acceleration while being rotated along with the drum, wherein the sensor controller is configured to control the sensor communication module to transmit an acceleration value corresponding to an output of the acceleration sensor, and wherein the main controller is configured to determine at least one of a load of laundry contained in the drum, or determine whether laundry contained in the drum is entangled, based on the acceleration value.