1. A software component reuse support method of supporting the use of existing software components when control software to be developed is created, using a specification database that stores the specifications of an existing device, a software component database that stores software components used in the control software of the existing device and the versions of the software components, an input device, and an arithmetic device, comprising: a likelihood analyzing step of allowing the arithmetic device to calculate a likelihood indicating the distribution of the frequency of use of each specification for each version of the software component, on the basis of the specifications of the device stored in the specification database and the software components and the versions of the software components stored in the software component database; a prior probability analyzing step of allowing the arithmetic device to calculate a prior probability indicating the distribution of the frequency of use of each version for each software component, on the basis of the specifications of the device stored in the specification database and the software components and the versions of the software components stored in the software component database; a specification input step of inputting the specifications of a device to be developed through the input device; a posterior probability analyzing step of allowing the arithmetic device to calculate a posterior probability indicating the reusability of each version of the existing software component for each specification of the device to be developed, on the basis of the specifications of the device to be developed, the likelihood, and the prior probability; and a software component selecting step of allowing the arithmetic device to select the version of the software component with a high posterior probability as a software component which can be reused for the control software of the device to be developed.