Unity標準UIのInputFieldはScroll出来ないので対処法 ref: http://qiita.com/divideby_zero/items/7cb32ac1c0b74be9ba6c

file0.cs

using UnityEngine;
using UnityEngine.Events;
using UnityEngine.UI;

public class ScrollableInputField : MonoBehaviour
{
    [SerializeField]
    private InputField _targetInputField;

    [SerializeField]
    private Button _guardButton;

    public UnityEvent OnFocus = new UnityEvent();

    void Start ()
    {
        _guardButton.onClick.AddListener(() =>
        {
            _targetInputField.ActivateInputField();
            OnFocus.Invoke();
        });
    }
}