The invention discloses an examination device, and specifically relates to a device for extracting fat in cakes. The device comprises: 1. a condenser pipe, 2. a pear-shaped flask, 3. a suction filtration cup. The operation is characterized by comprising the following steps: placing a sample in a filter paper cylinder, putting the filter paper cylinder into the suction filtration cup 3, adding a proper amount of diethyl ether into the pear-shaped flask 2 to make the liquid immerse the sample, putting the suction filtration cup 3 into the pear-shaped flash 2, installing the condenser pipe 1 on the suction filtration cup 3, keeping the interface hermetically sealed, putting the whole device into a water-bath with a temperature of 45 DEG C to carry out reflux for 1 hour, then removing the condenser pipe 1, lifting the suction filtration cup 3, washing the suction filtration cup 3 with diethyl ether, then pouring the diethyl ether solution in the suction filtration cup 3 into the pear-shaped flask, distilling the diethyl ether in the pear-shaped flask 2 under a negative pressure, and finally measuring the acid value and peroxide value of the residual fat.