https://www.motsuemon.com/shared/js/smoothscroll.js

1$(function () {
2        // PageTopヘッダ分ずらす
3        var headH = 0;
4
5        // PageTop
6        $('a[href^=#], area[href^=#]').not('a[href=#], area[href=#]').each(function () {
7                // jquery.easing
8                jQuery.easing.quart = function (x, t, b, c, d) {
9                        return -c * ((t = t / d - 1) * t * t * t - 1) + b;
10                };
11                if (location.pathname.replace(/^\//, '') == this.pathname.replace(/^\//, '') && location.hostname == this.hostname && this.hash.replace(/#/, '')) {
12                        var $targetId = $(this.hash),
13                                $targetAnchor = $('[name=' + this.hash.slice(1) + ']');
14                        var $target = $targetId.length ? $targetId : $targetAnchor.length ? $targetAnchor : false;
15                        if ($target) {
16                                var targetOffset = $target.offset().top - headH;
17                                $(this).click(function () {
18                                        $('html, body').animate({
19                                                scrollTop: targetOffset
20                                        }, 500, 'quart');
21                                        return false;
22                                });
23                        }
24                }
25        });
26                if (location.hash) {
27                        var hash = location.hash;
28                        window.scroll(0, headH)
29                        $('a[href=' + hash + ']').click();
30                }
31});