There is provided a concealed slide fastener. The slide fastener includes a pair of fastener tapes, a pair of fastener element rows, a slider, a box pin, a box body and an insert pin. The insert pin includes an insert portion configured to be inserted into a space of the box body and an engagement portion formed on a side surface of the insert portion, which faces the box pin and configured to be engaged with a lowermost one of the fastener elements of one of the fastener element rows which is close to the box pin. The length of the engagement portion is set to be at least twice an interval between the fastener elements.