1.Place potatoes in 3-quart saucepan; add enough water to cover potatoes. Cover and heat to boiling; reduce heat to low. Cook covered 25 to 30 minutes or until potatoes are tender; drain. Let stand until cool enough to handle. Cut potatoes into cubes.
2.Mix mayonnaise, vinegar, mustard, salt and pepper in large glass or plastic bowl.
3.Add potatoes, Japanese cucumber, corn and toss evenly