A connection detection device is mounted on an apparatus which has a circuit board with connectors and load circuits connected to the circuit board via each of the connectors. The connection detection device that detects a connection state between the circuit board and the load circuits includes a plurality of serial connection circuits in which pull-down resistors are connected in series with each of the connection detection signal lines wired to a predetermined contact of the connectors of the circuit board, wherein the pull-down resistors have different resistance values, a pull-up resistor connected to a parallel connection circuit in which the plurality of serial connection circuits are connected in parallel, a detection unit to detect voltage values of a connection point between the pull-up resistor and the parallel connection circuit, and a determination unit to determine the connection state between the circuit board and the load circuits by the detected voltage value.