How to stop player from flying off in the air? ,How to stop player from flying off in the air?

Hello,
My player is flying off in the air when I press space.
How can I fix/stop this?
Here Is my code:

using UnityEngine;
using System.Collections;
public class PlayerMovement : MonoBehaviour
{
public float speed = 5f;
public float jumpSpeed = 8f;
private float movement = 0f;
private Rigidbody2D rigidBody;
public Transform groundCheckPoint;
public float groundCheckRadius;
public LayerMask groundLayer;
private bool isTouchingGround;
// Use this for initialization
void Start()
{
rigidBody = GetComponent();
}

// Update is called once per frame
void Update()
{
    isTouchingGround = Physics2D.OverlapCircle(groundCheckPoint.position, groundCheckRadius, groundLayer);
    movement = Input.GetAxis("Horizontal");
    if (movement > 0f)
    {
        rigidBody.velocity = new Vector2(movement * speed, rigidBody.velocity.y);
    }
    else if (movement < 0f)
    {
        rigidBody.velocity = new Vector2(movement * speed, rigidBody.velocity.y);
    }
    else
    {
        rigidBody.velocity = new Vector2(0, rigidBody.velocity.y);
    }
    if (Input.GetButtonDown("Jump") && isTouchingGround)
    {
        rigidBody.velocity = new Vector2(rigidBody.velocity.x, jumpSpeed);
    }
}

}

I found it .
The Speed number should be reduced