Not running the script to display the date

Hi all!
When I put the script output from the current month in a custom Java script,

the result is not displayed in the place where I want to.

I use to output the \"span ID = ...\".

This is a script:

var currentmonth = document.getElementById("current_month");
function current_month() {
var today = new Date();
var month_of_year = ["Январь", "Февраль", "Март", "Апрель", "Май", "Июнь", "Июль", "Август", "Сентябрь", "Октябрь", "Ноябрь", "Декабрь"];
var year_ = today.getFullYear();
var month_ = month_of_year[today.getMonth()];
currentmonth.innerHTML = month_+' '+year_+' г. ';
setInterval(current_month, 1);

and output:

<span id="current_month">0</span>

What could be wrong?