1. A three-dimensional model generating method utilizing a calculator that generates a three-dimensional model based on measurement data, which includes measurement point group data obtained by measuring a measured object, a type of a plane element, and geometric values of the plane element, the method comprising: generating, via a three-dimensional model element generator, a three-dimensional model element representing a shape of at least a portion of the three-dimensional model based on the measurement data using a predetermined method, the three-dimensional model element being defined by a plane element and a predetermined condition; and generating, via a three-dimensional model generator, the three-dimensional model using one or a plurality of three-dimensional model elements, selecting, via the calculator and when generating the three-dimensional model, the predetermined plane element defining the three-dimensional model element from the measurement data; obtaining, via the calculator and when generating the three-dimensional model, the condition required to generate the three-dimensional model element; generating, via the calculator and when generating the three-dimensional model, the three-dimensional model element using the selected plane element and the obtained condition; and generating, via the calculator and when generating the three-dimensional model, the three-dimensional model of the measured object using one or a plurality of three-dimensional model elements.