Vagrant provisioning with Ansible fails

I'm trying to provision Ubuntu with Vagrant and Ansible. I'm working with this article and hit the error shown below.

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< TASK [Gathering Facts] >
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fatal: [default]: FAILED! => {"changed": false, "failed": true, "module_stderr": "Shared connection to 127.0.0.1 closed.\r\n", "module_stdout": "/bin/sh: 1: /usr/bin/python: not found\r\n", "msg": "MODULE FAILURE", "rc": 0}
 to retry, use: --limit @/Users/tomoya/vagrant-project/playbook.retry
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< PLAY RECAP >
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default                    : ok=0    changed=0    unreachable=0    failed=1

Ansible failed to complete successfully. Any error output should be
visible above. Please fix these errors and try again.

My directory's structure is:

vagrant-project
├── Vagrantfile
└── playbook.yml

Vagrantfile contains:

# -*- mode: ruby -*-
# vi: set ft=ruby :

Vagrant.configure("2") do |config|
  config.vm.box = "ubuntu/xenial64"
  config.vm.network "forwarded_port", guest: 80, host: 8080
  config.vm.provision :ansible do |ansible|
    ansible.playbook = "playbook.yml"
  end
end

playbook.yml contains:

---
- hosts: all
  sudo: true
  tasks:
    - name: update apt cache
      apt: update_cache=yes
    - name: install apache
      apt: name=apache2 state=present
    - name: install mysql
      apt: name=mysql-server state=present
    - name: install php
      apt: name=php5 state=present

I'm using:

• Vagrant 1.9.4
• VirtualBox 5.1.22
• Ansible 2.3.0.0

They are almost the same as the codes shown in the article. Could you please tell me what is wrong and how I could provision it successfully?

Thanks.