In order to enable controlling a transmit data volume within a proper range depending on variations in a communication environment, suppressing deterioration in utilization efficiency of a transmission bandwidth, and improving user perceived quality, a transmit data volume control method according to an exemplary aspect of the invention includes: acquiring a communication quality of a network, estimating a congestion degree of the network, determining a target congestion degree being a target of the congestion degree, based on the communication quality, and determining a transmit data volume, based on the congestion degree and the target congestion degree.