Abstract: A learning method for detecting unoccupied parking spaces by using probability distributions on decision points of the unoccupied parking spaces and relational linear segment information on relationships among the decision points is provided. And the method includes steps of: (a) a learning device performing (i) a process of instructing a first CNN to apply a first CNN regression operation to a parking circumstance image, to thereby calculate each of one or more estimated probability distributions, and (ii) a process of instructing a second CNN to apply a second CNN regression operation to the parking circumstance image, to thereby generate estimated relational linear segment information; and (b) the learning device instructing a loss layer to perform (i) a process training parameters in the first CNN by performing backpropagation using a first loss, and (ii) a process of training of parameters in the second CNN by performing backpropagation using a second loss.