A target supply device according to an aspect of the present disclosure includes a vibration element configured to generate a droplet by vibrating a target substance to be output from a nozzle 80, a droplet detection unit configured to detect the droplet, and a control unit 70. A first detection threshold and a second detection threshold to be compared with a detection signal from the droplet detection unit are set to the control unit 70. The first detection threshold is used to generate a light emission trigger for a laser beam. The second detection threshold has a smaller absolute value from a base line of the detection signal than the first detection threshold. The control unit 70 calculates an evaluation parameter for a satellite based on the detection signal and the second detection threshold, and determines a duty value of an electric signal suitable for operation of the vibration element based on the evaluation parameter.