The 96-year-old was driven on to the showground in a Range Rover.
After missing the State Opening of Parliament, there had been speculation that she would not attend the annual event, which is one of the highlights of her year.
She sat in the front passenger seat of the vehicle, casually dressed in a white blouse and a blue cardigan-style top and wearing sunglasses.
As the Range Rover pulled up near the parade ring, the Queen spoke to a small group, thought to be officials from the show, through the open car window.
She appeared relaxed, smiling and laughing as she chatted, while just a few feet away dozens of photographers tried to capture the moment.
Inside the parade ring, horses were put through their paces as classical music was played over the public address system.
Dozens of members of the public were also keen to have a memento of the occasion, holding up camera phones to record their glimpse of the Queen.
The monarch was last seen in public when she attended a service commemorating the life of her late husband, the Duke of Edinburgh, in March with senior royals and a congregation of hundreds.
She reached her Platinum Jubilee in February, overcame a bout of Covid after testing positive that month, and celebrated her 96th birthday on April 21 privately at her Sandringham estate.
Last October, she spent a night in hospital and over the following three months was under doctors' orders to only conduct light duties so missed a number of prominent events.
The Queen has been using a walking stick in public since she attended a service marking the centenary of the Royal British Legion last October.
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