To provide a clearance verification device facilitating clearance verification of a required part even when the design of a component is changed, a CAD system having the clearance verification device, and a computer program.

A target element specifying section 41 creates an infinite reference surface including the surface facing a reference component of a target component based on attribute information and arrangement condition information, selects a region including the reference component from the regions divided by the reference surface of an assembly, and sets it as a verification target region. The target element specifying section 41 excludes a region where the selected element of the target component exists on the reference surface. When the target element specifying section 41 determines that the element exists in the verification target region, the element is determined as a target element.

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