1. A subject estimation system comprising: a processor; and a memory having a computer program stored thereon, the computer program causing the processor to execute a convolution neural network, wherein the convolution neural network includes a convolutional layer including one or more topic-dependent convolutional layers and one topic-independent convolutional layer, each of the one or more topic-dependent convolutional layers performing, on an input of a word-string vector sequence corresponding to dialog text transcribed from a dialog, a convolution operation dependent on a topic, and the topic-independent convolutional layer performing, on the input of the word-string vector sequence, a convolution operation not dependent on the topic, a pooling layer performing pooling process on outputs of the convolutional layer, and a fully connected layer performing full connection process on outputs of the pooling layer and estimating a subject label of the dialog.