The Judicial branch
executive
The Executive Branch and the Judicial Branch can grant pardons in the United States. It is usually a governor of a state who will grant a pardon for a person who is incarcerated. The President of the United States might also grant pardons.
According to current laws (and this should be in the Constitution as well), the Executive Branch, specifically the President of the United States, is allowed the 'power of pardon' (the ability to grant pardons).
the judicial branch
By appointing Article III federal judges to the Judicial Branch, and by granting pardons (may not grant a pardon for an impeachment).
The Executive branch. Or, more specifically, the President of the United States.
Pardons
The judicial branch of government is the branch of government that grants reprieve or pardons. Reprieves are usually granted at the federal level of the court system.
The Executive Branch.More specifically, the President can grant pardons to whom whoever, whenever he wishes. This excuses the person of their crime and conviction that the President pardons.
The Executive branch of government is the only branch that can grant pardons and reprieves, under Article 2, of the United States Constitution. Only the President has the ability to grant pardons and reprieves in the Executive branch.
He actually isn't checking any branch of the government. He is simply exercising a unique power granted to his office.