What gland in the body produces insulin?

The Pancreas.

The pancreas is a large gland situated below and behind the stomach in the lower abdomen. The pancreas secretes pancreatic juice into the duodenum (the first section of the small intestine) through the pancreatic duct. The digestive enzymes in this juice help break down carbohydrates, fats, and proteins.

Scattered among the cells that produce pancreatic juice are small groups of endocrine cells. These are called the Islets of Langerhans. They secrete two hormones, insulin and glucagon, which maintain blood glucose (sugar) levels.

Insulin is secreted in response to high glucose levels in the blood.

It lowers sugar levels in the blood by increasing the uptake of glucose into the tissues. Glucagon has the opposite effect. It causes the liver to transform the glycogen (a carbohydrate) it stores into glucose, which is then released into the blood.