Button does not function on the first click

function showCheckbox(){  
    var node_list = document.getElementsByClassName('check');
    for (var i = 0; i < node_list.length; i++) 
    {  
      if(node_list[i].style.display == 'none') { 
        node_list[i].style.display = 'block';
      } else { node_list[i].style.display = 'none'; }
    }
}

input[type=checkbox]{
display:none;
position:relative;
}

<input type="button"  value="Εμφάνιση" onclick="showCheckbox()" /><img src="form-images\trash.png"  onclick="" style="width:21px;height:24px;margin-left:20px; "/><input type="checkbox" class="check" />   <label>Ψάρεμα</label><input type="text"  /></br><input type="checkbox" class="check" />   <label>Γήπεδο</label><input type="text"/></br>