Sub SplitAtVertex()
  Dim pMxDoc As IMxDocument
  Dim pFeatureClass As IFeatureClass
  Dim pFeatureLayer As IFeatureLayer
  Dim pFeatureCursor As IFeatureCursor
  Dim pOutFeatureCursor As IFeatureCursor
  Dim pFeature As IFeature
  Dim pOutFeatureBuffer As IFeatureBuffer
  Dim pSegmentCollection As ISegmentCollection
  Dim pSegment As ISegment
  Dim pPointCollection As IPointCollection
  Dim i As Integer

  'TOCで選択したレイヤのラインを分割します。
  Set pMxDoc = ThisDocument
  If Not pMxDoc.SelectedLayer Is Nothing Then
    Set pFeatureLayer = pMxDoc.SelectedLayer
  Else
    MsgBox "分割するレイヤを選択してください"
    Exit Sub
  End If

  Set pFeatureClass = pFeatureLayer.FeatureClass
  Set pFeatureCursor = pFeatureClass.Update(Nothing, False)
  Set pOutFeatureCursor = pFeatureClass.Insert(True)
  Set pFeature = pFeatureCursor.NextFeature

  '全フィーチャをループ処理します。バーテックスで各フィーチャを分割し、
  '属性と図形を新規フィーチャにコピーします。
  Do While Not pFeature Is Nothing
    Set pSegmentCollection = pFeature.Shape
    For i = 0 To pSegmentCollection.SegmentCount - 1
      Set pSegment = pSegmentCollection.Segment(i)
      Set pOutFeatureBuffer = pFeatureClass.CreateFeatureBuffer
      AddFields pOutFeatureBuffer, pFeature
      Set pPointCollection = New Polyline
      pPointCollection.AddPoint pSegment.FromPoint
      pPointCollection.AddPoint pSegment.ToPoint
      Set pOutFeatureBuffer.Shape = pPointCollection
      pOutFeatureCursor.InsertFeature pOutFeatureBuffer
    Next i
    pFeatureCursor.DeleteFeature
    Set pFeature = pFeatureCursor.NextFeature
    pOutFeatureCursor.Flush
  Loop
  pFeatureCursor.Flush
  'Refresh
  pMxDoc.ActiveView.Refresh
End Sub

Private Sub AddFields(pFeatureBuffer As IFeatureBuffer, pFeature As IFeature)
  '元フィーチャから新規フィーチャに属性をコピーします。
  Dim pRowBuffer As IRowBuffer
  Dim pNewFields As IFields
  Dim pNewField As IField
  Dim pFields As IFields
  Dim pField As IField
  Dim i As Integer
  Dim NewFieldIndex As Long

  Set pRowBuffer = pFeatureBuffer
  Set pNewFields = pRowBuffer.Fields

  Set pFields = pFeature.Fields
  For i = 0 To pFields.FieldCount - 1
    Set pField = pFields.Field(i)
    If Not pField.Type = esriFieldTypeGeometry And Not pField.Type = _
    esriFieldTypeOID And pField.Editable Then
      NewFieldIndex = pNewFields.FindField(pField.Name)
      If Not NewFieldIndex = -1 Then
        pFeatureBuffer.Value(NewFieldIndex) = pFeature.Value(i)
      End If
    End If
  Next
End Sub