SHDocVwSample09

test.cs

public void CheckCheckBox()
{
    var IE = new SHDocVw.InternetExplorer();
    IE.Visible = true;
    object URL = "http://law.e-gov.go.jp/";
    IE.Navigate2(ref URL);
    IE.Wait();
    var doc = IE.Document as mshtml.IHTMLDocument3;
    //1つ目の方法
    foreach (mshtml.HTMLInputElement ele in doc.getElementsByName("H_YOMI_GUN")) //item(index: ) では指定できず…（謎
    {
        if (ele.value == "3") { ele.click(); } //valueの値を見て選択
    }
    //2つ目の方法
    foreach (mshtml.HTMLInputElement ele in doc.getElementsByName("H_RYAKU"))
    {
        if (ele.value == "2") { ele.setAttribute("checked","checked"); } //valueの値を見て選択 (方法その２)
    }
}